Bundesliga leaders Bayern Munich will kick-off the second half of the German league season at Bayer Leverkusen on Friday without star striker Robert Lewandowski and key defender Mats Hummels.

Bayern hold a commanding 11-point lead over their nearest German league rival, but fourth-placed Bayer Leverkusen are on a 12-match unbeaten run dating back to September in all competitions.

Bayern will be missing key stars.

Lewandowski, the Bundesliga's top-scorer with 15 goals in 17 games so far, is labouring with a knee injury while Hummels has a groin strain and the away match at Leverkusen's BayArena has come too early.

"Both have been taking part in team training and we will only increase their training schedule on Monday, anything else would be negligent," said Bayern head coach Jupp Heynckes in Thursday's press conference.

With Lewandowski out, burly Germany striker Sandro Wagner is set to make his first Bundesliga appearance since joining from Hoffenheim last month, reportedly for 12 million euros ($14.3m).

"It doesn't really change much, he (Wagner) is a player who can play with his back to opponents and secure possession, just like 'Lewy'," said Heynckes.

In Hummels' absence, Heynckes will most likely pair Niklas Suele and Jerome Boateng at centre-back.

Bayern were five points adrift in the league when Heynckes, 72, replaced Carlo Ancelotti at the start of October, but built up a commanding lead as key rivals RB Leipzig and Borussia Dortmund faltered.

"We worked hard for the lead, also with some help from the competition, you have to admit that," said Heynckes.

"We have to keep working hard, looking at the table won't get us anywhere."

Bayern ran out comfortable 3-1 winners over Leverkusen when the teams last met in Munich in August, but Heynckes' side last won away at Leverkusen in 2013.

"They are a young, hungry and highly talented side, which has a lot of imagination," said Heynckes.

"It's a game which has all the ingredients that make football so attractive, both teams can play good football and it's going to be tough."

Leverkusen's Jamaica winger Leon Bailey, 20, made a name for himself in the first half of the season with six goals and four assists.

However, Heynckes warns there is plenty of talent in Bayer's ranks, pointing to Germany winger Julian Brandt and teenager Kai Havertz, 18, who are both dangerous in front of goal.

"They are also strong in defence and are a convincing team, that is why they have gone 12 games without a defeat," added Heynckes.

Having also steered the club to the 2013 treble of Champions League, Bundesliga and German Cup titles, Bayern's bosses want to keep Heynckes on, but he insists he will leave - as promised - when the season finishes in May.

"I have said everything there is to say and won't say anything more," replied Heynckes when asked about his future in the midst of Bayern's hunt for a new head coach for 2018/19.