Goretzka a doubt for Bayern's trip to Berlin

The 23-year-old Germany international, normally a central midfielder, replaced David Alaba at left-back for Tuesday's 1-1 draw at home to Augsburg, but twisted his ankle while fouling Andre Hahn after only 13 minutes and was replaced by eventually Alaba at the break.

"I hope it's not too serious," Goretzka told reporters.

An Arjen Robben goal for the hosts at Munich's Allianz Arena was cancelled out when Augsburg substitute Felix Goetze, the younger brother of fallen Germany star Mario, scored four minutes from time against his former club having only left Bayern in July.

Leaders Bayern can extend their lead at the top of the Bundesliga table to five points with a win over third-placed Hertha at the Olympic Stadium.

However, Goretzka could miss out, "because he has a fat ankle," according to Bayern coach Niko Kovac.

Kovac praised Goretzka's efforts but the rising Germany star was less than impressed after what was his 120th Bundesliga appearance.

"I was not satisfied, it is clear that I can't do what David Alaba does and smash over a cross from the left," said Goretzka, who joined Bayern from Schalke in the off-season.

"It wasn't a good game from me."

The draw cost Kovac the record of eight straight wins in all competitions at the start of his tenure as Bayern coach, but Goretzka says conceding the late equaliser was "perhaps it was a wake-up call at the right time" for the squad.