The midfielder is adamant the Polish striker will still give his all for the club despite frequent rumours linking him with a move to Bayern Munich
The Poland international was close to joining Bayern Munich this summer, however, the deal fell through as BVB CEO Hans-Joachim Watzke decided to keep the star for another season.
"We have a superb team with a great atmosphere among the squad," the 24-year-old told reporters at a press conference in Bad Ragaz.
"Robbie is committed and gives everything. He's the same he has always been."
Bender then went on to praise "the fastest offence" he has ever played behind but warned that his team should also focus on stabilising the defence as well to avoid conceding as many goals as last season.
"If you concede less, you need to score less in order to win. Therefore, we must act focused and disciplined at the back," he added.
"If we're able to do that, we can beat any opponent."
Lewandowski's contract with Jurgen Klopp's side expires in June 2014 and he has already intimated he could join Bayern at the end of next season.