"English clubs continue to take advantage of the opportunity to strengthen their teams with capable players. One of the former Glasgow leaders, striker Chris Sutton, is moving to a team without a transfer fee.
The 32-year-old Englishman left the Glasgow team by mutual agreement. The contract with Birmingham will be valid until the end of the season.
"Of course, we are very disappointed to lose a player of Chris' caliber," said Celtic coach Gordon Strachan. "The club satisfied the player's desire to leave, and I would like to wish him success in the future."
Birmingham has been trying to attract Swedish forward Henrik Larsson to their team for some time, as they have been unable to find a replacement for one of their leaders, Samuel Eto'o, who will soon leave to play in the African Cup of Nations tournament due to a recent serious injury.
"It was very difficult for me to leave Celtic," said C. Sutton. "But given the circumstances, I had no other choice. I spent five years with the team under the leadership of Martin O'Neill. I want to thank all the players and staff for the warm welcome me and my family received."
C. Sutton arrived at Celtic in 2000 after an unsuccessful season in another team. The footballer, who cost 6 million pounds, scored 86 goals in 199 matches wearing the Scottish team's jersey.