Aiden McGeady has left Celtic and joined Spartak Moscow on a four-year contract.
The Republic of Ireland international had been linked with a move to England, but will now head to eastern Europe in a deal believed to be close to £10million.
"The Celtic fans are second to none and it is a fantastic club to play for."
He added: "Celtic is the team I have supported my whole life and will miss so many things, however I am looking forward to the challenge of playing for Spartak Moscow.
"I wish the current players and management all the very best for the season ahead and I will be back whenever I can to cheer the team on."
Hoops boss Neil Lennon commented: "I would like to wish Aiden all the best with his move to Spartak Moscow.
"It is obviously a disappointment to lose a player with Aiden's talent. However, it was his desire to try and further his career in pastures new and I respect his decision.
"Spartak Moscow are a good club and I am sure Aiden will do very well there.
"I would like to wish Aiden and his family the very best of luck for the future."