Dortmund's Philipp sidelined for 'several months'
The forward sustained the problem in the opening 10 minutes of the 1-1 Bundesliga draw at the BayArena, and was carried from the field on a stretcher.
Dortmund have confirmed the severity of the problem, which looks likely to rule the 23-year-old out for the remainder of the campaign.
"Maximilian Philipp is missing unfortunately for several months," the club announced via their official Twitter account.
"The offensive player suffered a serious knee injury involving the kneecap in the Bundesliga game last Saturday in Leverkusen. Milli, we wish you get well soon!"
Maximilian #Philipp wird dem BVB leider mehrere Monate lang fehlen. Der Offensivakteur erlitt im Bundesliga-Spiel am vergangenen Samstag in Leverkusen eine schwere Knieverletzung unter Beteiligung der Kniescheibe. Milli, wir wünschen dir gute Besserung! pic.twitter.com/9jWh63fboN
— Borussia Dortmund (@BVB) December 5, 2017
After arriving from Freiburg in the off-season, Philipp has netted six goals in 11 league outings for Peter Bosz's side.