The French winger has had pain in his legs and is facing a race against time to be fit for Friday's clash against Gladbach after the Bundesliga's winter break.
The France winger has returned to training ahead of the resumption of the Bundesliga season after missing friendlies against Al Kuwait and Red Bull Salzburg.
However, Bayern coach Guardiola revealed the former Marseille man is an injury concern for the trip to third-placed Gladbach.
"He had pain in his legs in the last days. Today we have the last training, until now I still do not know whether he can play tomorrow," the Spaniard is quoted as saying by Kicker.
One player who will definitely not feature at Borussia-Park is midfielder Bastian Schweinsteiger, who has been out since November due to an ankle injury and is now suffering with a knee problem.
Schweinsteiger is not yet ready to return, but Guardiola hopes to have the influential Germany international back in the near future as the Bavarian giant continues its pursuit of more silverware.
"He is one of the best players in the league in recent years. We need him, it is a pity for us and for him that he has been able to play so little," the former Barcelona coach said.
Winger Arjen Robben, who turned 30 on Thursday, and versatile captain Philipp Lahm will return to the squad for the clash with Gladbach.
Guardiola is expecting a stern test from Lucien Favre's side, which is unbeaten in eight league games.
He added: "If we don't put all of the things that set us apart into action, then we will have problems."