Bayern coach Pep Guardiola told Sky Sports that the 22-year-old will probably need an operation after partially tearing the medial ligament in his left knee in the 3-3 Bundesliga draw at home to Hoffenheim on Saturday.

"We will miss Thiago, he is a special player in midfield," said Guardiola.

The injury will keep attacking midfielder Thiago out of both Tuesday's first leg at Old Trafford and the return at Munich's Allianz Arena on April 9.

The Spain star also faces a race against time to be fit for the Champions League semi-finals at the end of April, should Bayern progress.

The German and European champions expect an exact diagnosis after a scan on Sunday.

Thiago, who joined Bayern from Barcelona in July, limped off after 25 minutes and was replaced by captain Philipp Lahm, who was one of several stars rested from the starting line-up ahead of the Manchester trip.

Despite the draw, Bayern still remain 22 points clear in the table and extended their record unbeaten Bundesliga run to 53 matches.