Bayern Munich boss Julian Nagelsmann says he is unsure why Leroy Sane has struggled for form this season, acknowledging that the winger has been far from his best in recent weeks.

However, Nagelsmann also hailed Sane's "incredible qualities' and backed him to improve, rejecting criticism of his frustrated reaction to being substituted in a 1-0 win over Augsburg.

Sane played 65 minutes of the Bundesliga leaders' hard-fought victory but managed just one shot and four touches in the visitors' penalty area before being replaced by Kingsley Coman.

A late penalty from Robert Lewandowski was enough to extend Bayern's unbeaten league run to seven games, but the former Manchester City winger's below-par display marked his fifth consecutive league game without a goal.

After the victory, the Bayern coach admitted he was perplexed by Sane's poor form but backed him to get back to his best and hailed the 26-year-old's "incredible" ability. 

"I like Leroy very much, as a person and as a player. Everyone knows that he has incredible qualities," Nagelsmann said.

"He is self-critical enough and knows himself that he hasn't recently played well. I don't know exactly why.

"He's had ups and downs throughout his career. I support him completely."

Sane has scored seven goals in 28 Bundesliga appearances this season, with only Lewandowski (32) and fellow winger Serge Gnabry (11) netting more often for the perennial champions. 

However, the latest of Sane's league goals came in a 1-0 win over Eintracht Frankfurt in mid-February, and the 26-year-old cut a frustrated figure when replaced against Augsburg, appearing to shake Nagelsmann's hand half-heartedly before making his way to the bench.

Nagelsmann, however, refused to criticise Sane for his reaction, and was keen to move swiftly on from the incident.

"I'm not angry, we don't have to make a headline out of it," Nagelsmann added.

Bayern are back in Champions League action on Tuesday as they attempt to recover from a 1-0 first-leg loss to Villareal when they welcome Unai Emery's team to Bavaria.

Sane has been in much better form on the European stage, recording six goals and six assists in the competition this season. Since Opta records began in 2003-04, those 12 goal contributions are the joint-most managed by a German player in one Champions League campaign, along with Mario Gomez in 2011-12 (12 goals, also playing for Bayern).