The Hoops won back the league title, while Rangers reached the Europa League final and went one better in the Scottish Cup.
It should be another close title race next season, and both clubs will be doing everything in their power to make that happen by investing this summer.
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Celtic and Rangers will be keen to strengthen to avoid falling behind their biggest rival, and with that in mind, we have rounded up all the latest transfer news and rumours concerning both clubs.
Semedo deal
Celtic look set to secure a deal for Alfa Semedo.
According to Diario de Transferencias, the Hoops are about to complete a loan deal for the Vitoria Guimaraes midfielder.
But while the deal is an initial loan, the report claims there is also an obligation to buy worth €2.5m with a further £1m in add-ons.
Juranovic exit talk
Fabrizio Romano has suggested there could be a key exit from Parkhead this summer.
He tweeted: “Croatian national team right back Josip Juranovic is expected to leave Celtic FC this summer as many clubs are following him. Jurankvic is attracting interests from Premier League clubs too after great season for club and country. “
Since then, it has emerged Celtic would want at least £15million and that the player is happy where he is for now.
Sale talks
Rangers are being backed to sell striker Alfredo Morelos ahead of next season.
According to Fanatik, the Gers are locked in discussions over selling the striker, who has one year remaining on his contract.
And club chief Ross Wilson is said to be ‘scrambling’ to secure the best deal for the club.
Rangers will need to raise a good fee to adequately replace the frontman this summer.