Milan's midfield playmaker Andrea Pirlo has flown to Barcelona to see a specialist about his latest knee injury.
The 31-year-old Italy international was due to make his comeback against Parma on Saturday, but strained his knee badly in training the day before.
He is now expected to be out of action for at least six weeks.
La Gazzetta dello Sport understands Pirlo has sought the advice of Ramon Cugat, who operated on his teammate Filippo Inzaghi earlier this season.
Cugat has worked with some of the world's great players such as Samuel Eto'o, Antonio Di Natale and Zlatan Ibrahimovic.