No indication has however been declared as to how long the Finland international striker will be sidelined for.
A statement on the official Chelsea website reads: "Mikael Forssell underwent knee surgery yesterday, watched by Chelsea physio Mike Banks, and his recent problem was successfully diagnosed and treated.
“It was a simple surgical procedure. He requires quality rest now, then there’s a clear rehabilitation programme, and he could be back before the end of the season," Banks says.
"It was decided that Mikael would return to Chelsea from Birmingham for treatment last week. His loan, however, continues until the end of the season."