Former Parkhead chief executive Peter Lawwell and ex-Light Blues director of football Mark Allen both had a significant role in their clubs’ recruitment policies.
There have been some memorable arrivals, large transfer fees and some unmitigated disasters.
Here, GlasgowWorld compile a list of the top-ten biggest Old Firm flops over the last ten years.
10. EDUARDO HERRERA (Forward) - £1.5m from Pumas U.N.A.M in June 2017
Former Rangers manager Pedro Caixinha was eager to bring the Mexican international to Ibrox but the move proved to be an expensive disaster as he failed to win any fans over during his time Glasgow.
The striker scored just one goal in the Scottish Premiership against Ross County during his nightmare spell, making just 21 appearances, of which 17 of them were from the bench.
He spent time the following two seasons out on loan at Santos Laguna and Club Necaxa in his homeland before the Gers could finally clear his name off their wage bill. Currently playing for Venados FC in Mexico.
9. AMIDO BALDE (Forward) - £1.8m from Vitoria Guimaraes in June 2013
An impressive physical specimen on paper standing at 6ft 4in, who drew comparisons to Emmanuel Adebayor but in hindsight he didn’t come close to the former Arsenal and Manchester City striker.
After signing on a long-term deal, it was hoped the Guinea-Bassau internationalist could cause a significant threat to opposition defences and prove to be a regular goal scorer, but it soon became clear he was never going to be of the required standard to lead the Hoops frontline.
His contract was terminated two years early in 2015 following a loan spell in Belgium with Waasland-Beveren. Currently plying his trade in Vietnam with Ho Chi Minh City FC.
8. FRANCISCO SANDAZA (Forward) FREE from St Johnstone in August 2012
It was clear from the outset that the Spaniard never wanted to be at Rangers in the first place. Just six months after turning down an initial pre-contract deal, the enigmatic striker then opted to change his mind and sign a three-year-deal.
He arrived at Ibrox after the club were sent to the bottom of the Scottish Football pyramid following successful spells with Dundee United and St Johnstone.
Sandaza failed to get regular game-time and was sensationally SACKED by the club after he was caught up in a scandal involving a Celtic-supporting hoax caller who posed as a football agent and recorded the player admitting he was interested in moving to the MLS. Undoubtedly one of the strangest moments in the Rangers history. Was last spotted playing in the Indian Super League with Hyderabad.
7. DERK BOERRIGTER (Midfielder) - £3m from Ajax in July 2013
The Dutchman was dubbed by Ajax fans as “sicknote” due to his frequent trips to the treatment table and that in itself should have been a warning sign to the Hoops.
His debut against Ross County ended prematurely as he hobbled off injured and his Parkhead career was plagued with numerous setbacks thereafter.
The winger was unable to adapt to the system Neil Lennon was keen to enforce and it quickly became apparent he would do well to see out his four-year deal. Boerrigter was reportedly on an impressive wage packet but he was forced to hang up his boots after failing to recover from an ankle problem, which he later blamed the Celtic medical staff for misdiagnosing. Quietly released by the club in April 2016.
6. JOEY BARTON (Midfielder) FREE from Burnley in May 2016
A well-renowned figure during his time in England, the midfielder made the bold statement he was coming up to Scotland “to be the best player in the country.” It never turned out that way!
His Rangers league debut came against Hamilton Academical and he was left red-faced after being nutmegged by Ali Crawford.
Four months after his arrival, Barton was suspended by the club for three weeks after a training ground argument with Andy Halliday and that spelled the end of his Gers career as he had his contract terminated in November. Took his first steps into management with Fleetwood Town in 2018 and is currently in charge of League Two Bristol Rovers.
5. MARIAN SHVED (Midfielder) £1.7m from Karpaty Lviv in 2019
Brendan Rodgers claimed he had never heard of the Ukrainian winger before when he was first linked with the player and the writing was on the wall as soon as he arrived in Glasgow.
Shved made just three substitute appearances for the Hoops, scoring against Nomme Kalju in a Champions League qualifier and was contracted until 2023 but he exit was finally confirmed during the summer as he completed a permanent move to Belgian club KV Mechelen.
4. CARLOS PENA (Midfielder) £3.2m from C.D. Guadalajara in June 2017
Arrived at Ibrox on the same day as fellow flop Eduardo Herrera, the Mexican boasted a decent reputation after enjoying success with Leon in his homeland, but he just could never seem to settle in Glasgow.
Pena was said to have been dealing with personal issues that was affecting his form on the pitch and it meant he was limited to just 12 appearances for Rangers.
His Rangers career was over, but the club struggled to get the player off their books as they shipped him out on two separate loan spells to Cruz Azul and then Necaxa. His contract was eventually terminated in February 2019. Has racked short stints at further five clubs since leaving Ibrox, where he is most recently contracted to Antigua Guatemala FC.
3. VASILIS BARKAS (Goalkeeper) - £5m from AEK Athens in July 2020
The Greek shot-stopper appears surplus to requirements just 13 months after he arrived at Parkhead in a bid to nail down the No.1 spot.
After making a series of horrendous blunders, new Celtic manager Ange Postecoglou moved quickly to add the experienced Joe Hart in a desperate bid to resolve the club’s goalkeeping crisis and it already seems unlikely Celtic will be able to re-coup anywhere near the money they spent on Barkas.
Was attracting interest from his former club AEK and PAOK during the summer but a move never materialised.
2. UMAR SADIQ (Forward) LOAN from AS Roma in July 2018
The Ibrox club reportedly shelved out a six-figure fee to bring the striker in on a season-long loan from the Serie A outfit, but he turned out to be a massive disappointment.
Expectation levels were high when the Nigerian first arrived, but he failed to get off the mark in just four appearances.
His solitary start came against Aberdeen in the Scottish League Cup semi-final but despite seemingly being clean through on goal, the frontman performed a theatrical dive in the hope of winning his side a penalty – summing up her entire Gers career.
Steven Gerrard lost patience with him and Sadiq was allowed to leave before his deal was scheduled to come to an end. Amazingly, his price tag has somehow risen dramatically in recent years after a successful time at Partizan Belgrade, which has seen him linked with Sevilla and Manchester City in recent months.
1. SHANE DUFFY (Defender) - £2m (loan) from Brighton & Hove Albion in September 2020
The Republic of Ireland internationalist admitted it was a “dream” to join the club he grew up supporting in a high-profile loan deal from English Premier League club Brighton to aid Celtic’s pursuit of a historic ten-in-a-row.
Brought in to add a bit of steel to the Hoops rear-guard, his start to life in Glasgow began well with goals in his first two games against Ross County and St Mirren, but things went downhill rapidly.
The defender’s underwhelming performances impacted badly on the team as he continued to make mistake after mistake as the Hoops toiled domestically and in Europe.
With his confidence clearly shot to pieces, Duffy lost his place in Neil Lennon’s side to youngster Stephen Welsh and it’s safe to say Hoops supporters were happy to see the back of the centre-half. Has since re-built his belief and is grasping his second chance at Brighton.