By Oliver Trust

BERLIN, Jan. 29 (Xinhua) -- Bayern Munich's star striker Robert Lewandowski is concerned his side's negligent performance in the German Bundesliga could have a negative effect on the club's performance in the Champions League.

"It does not matter how big the lead is, [what's] important is the mental and physical state of the team. We all know it is not easy to play the national league with only 80 to 90 percent and then perform at 100 percent in the Champions League," the 29-year-old Polish international said.

Despite the Bavarians ruling the Bundesliga with a 16-point lead over their nearest rivals Bayer Leverkusen, it is time to ring the bell, Lewandowski says. "We all know what happened in the Champions League [in the last few] years when we ended up as national champion many points ahead of the [nearest] opponents," the striker stressed.

Lewandowski said the years after the team won the treble in 2013 were far from perfect. It caused deep disappointment not to have made it to the final again. "It does not help to be 16, 20 or 25 points ahead in the league; [what's] important is to be ready for the shoot-out in the Champions League," Lewandowski said. He also demanded a more consistent performance in the Bundesliga to be prepared for the challenging tasks in the Champions League.

Bayern coach Jupp Heynckes still rejects congratulations for the 2018 German title; others are much more open to good wishes. "I don't expect us to spoil the thing and looking at our quality I don't think it is going to be a nail-biter in the end," German international Thomas Mueller emphasized.

But like Lewandowski, Mueller demanded full concentration and everybody keeping their feet on the ground ahead of the Champions League challenge. "We have to fight sloppiness with all our energy," Mueller emphasized.

Heynckes said he is aware of the difficulties his team has had to deal with. "We will continue with our work based on full concentration. And we will not allow anyone to lean back and not give 100 percent," the 72-year-old commented.

Heynckes said conceding five goals in three games is not up to his standards. The 2013 treble winner demanded improvement regarding the team's defensive performance. "We need to be organized better in front of our goal and keep clean sheets. This is inevitable when looking at the challenges waiting in the Champions League and the bigger clubs we have to face," Heynckes stressed.

In the last 16 of the 2017/2018 Champions League campaign, the Bavarians are facing the Turkish side Besiktas Istanbul on February 20th and March 14th.

After beating TSG Hoffenheim 5-2 last weekend, Heynckes was not satisfied with the team's performance. "We allowed too much space for the opponents in midfield," said goalkeeper Sven Ulreich. Mueller called the 16th victory this season "far from ideal".

Heynckes warned his stars to give 100 percent "as only the performance counts not names and success of the past." Otherwise, stars could well find themselves sidelined. Heynckes has changed the team's lineup in several Bundesliga games. "We are not worried as we have enough quality in the squad, but we have to prove that quality every week in every game," Heynckes said.

Heynckes renewed his decision to leave the club at the end of the season despite an offer from the club.