Bayern Munich face mounting injury problems ahead of Saturday's showdown with Union Berlin, as Hansi Flick fears Niklas Sule could miss the second leg with Paris Saint-Germain in the Champions League.

Sule, Leon Goretzka, Lucas Hernandez and Marc Roca will all be absent when Bayern return to Bundesliga action at the weekend.

Defender Sule and midfielder Goretzka were both injured in the 3-2 quarter-final first-leg loss to PSG, with the former a major doubt for the return match.

"Leon Goretzka, Niklas Sule, Lucas Hernandez and Marc Roca will all be unavailable," said head coach Flick.

"Niklas Sule and Leon Goretzka have muscular problems. Leon's problems aren't quite as bad as Niklas'.

"So Niklas will probably miss the second leg versus PSG as well. We need to wait and see how things develop.

"Marc got injured against Leipzig. He started training again but had to stop. Lucas suffered a knock, this is nothing to do with his abdominal muscle injury, but it's painful.

"We're hoping Leon and Lucas will be available in Paris."

Despite Bayern's midweek setback in defence of their Champions League title, Flick's men sit seven points clear at the Bundesliga summit ahead of the visit of seventh-placed Union Berlin.

Union held the German champions to a 1-1 draw in December and Flick expects another tough test from Urs Fischer's side.

"We want to beat Union, but it will be difficult," he said. "We will also be taking workload into consideration however, but three points are our priority.

"I like their mentality and the way they play football. They run a lot and are very dynamic. The coach is doing an outstanding job and I'm looking forward to seeing him again."