The Bhoys forward took to social media after the 5-0 win over Inverness Caledonian Thistle.
Celtic beat Inverness 5-0 to finish the Scottish Premiership season in style, having ended the campaign as league champions.
And Guidetti, on loan with the Hoops for the season, was delighted to have won two trophies during his time at the club (Celtic also lifted the Scottish League Cup).
However, the Swede's tone suggested this was a goodbye message. The striker hasn't agreed a new contract with Celtic yet and his current deal at Manchester City expires at the end of the season.
Guidetti could end up staying with the Scottish champions but it doesn't quite appear that will be the case at present. The 23-year-old was predominantly speaking in past tense and looks as though he will leave the Bhoys.
He wrote: "I just Wanna say thank you to all the players and staff of#Celtic and also to all the wonderful fans ! It's been an amazing year I won my first 2 titles, I meet so many amazing peapole but best of all I got 2 play in a full Celtic park on a European night witch Celtic are known for all around the world! So thank you once again I am very proud and so happy to have played for Celtic ! God bless averyone ! #hail #hail."
Guidetti started the season brilliantly with Ronny Deila's side but fell out of favour and has often been criticised for his attitude.
Wherever the Swede will end up, though, he will be remembered fondly by many, with a lot of the replies from fans on his Instagram post generating kind and warm comments.