Thomas Muller will start Bayern Munich's clash with title rivals Union Berlin on Sunday after he was hauled off early on in the defeat to Borussia Monchengladbach.

Head coach Julian Nagelsmann replaced captain Muller with Joao Cancelo after just 16 minutes against Monchengladbach, making a tactical substitution with Bayern a goal behind and down to 10 men after Dayot Upamecano's early red card.

The champions went on to lose 3-2, another blow to their hopes of winning an 11th consecutive Bundesliga title as their challengers made ground.

Nagelsmann's decision to replace veteran Muller so early came under scrutiny after the match, having also chosen to start him on the bench for Bayern's 1-0 Champions League first-leg victory over Paris Saint-Germain.

With the Bavarian side facing shock title challengers Union this weekend, Nagelsmann confirmed the 33-year-old will be in the starting XI.

"Thomas is a very experienced player, he was told why the decision was made," Nagelsmann said at his pre-match press conference. "You can always discuss it afterwards. I spoke to Thomas at length and clearly he is not happy.

"He is very professional and an important player. His importance is huge because it goes beyond the game itself. He will start on Sunday. He is aware of the overall situation."

The slip-up against Monchengladbach allowed Borussia Dortmund and Union to both pull level on points with Bayern at the top, though the champions' goal difference means they clung onto their position at the summit.

Nagelsmann's men have picked up just nine of a possible 18 points since the turn of the year, while Sunday's opponents have taken 16 over the same period.

A tricky encounter is expected against Union, who have never won a Bundesliga match against Bayern in seven attempts.

"I'm expecting a top game," Nagelsmann said. "Union always bring their football onto the pitch, designed for counter-attacks, with their physicality. It's always uncomfortable to play them.

"It will definitely be an exciting and interesting game, hopefully with a better outcome for us."

Nagelsmann revealed Bayern could be boosted by the return at some point in the game of Sadio Mane, who has been absent since early November after suffering a leg injury that ruled him out of Senegal's World Cup campaign.

"Sadio Mane isn't fit enough to start," Nagelsmann added. "But he is an option that we're really happy about."