The 24-year-old Pole is on the radar of a number of Europe's top clubs, with Bayern Munich, Chelsea and Manchester United all vying for the services of the marksman.

Media speculation in Germany has been rife that Lewandowski is unsettled at the Westfalenstadion, but that appears to be news to Bender, who has no doubt that if the Polish striker stays in Dortmund this season, Lewandowski will give his all for the cause.

"I don't know if it looks like Robert Lewandowski is not in a good mood, but to me he seems pretty much normal and it doesn't feel different to before," Bender said.

"There is not much to say about it. Robbie is well committed, working hard and the same Robbie as always."

Bender has also hailed new signing Pierre-Emerick Aubameyang, saying the striker - a €13 million acquisition from French club Saint-Etienne - is the fastest player he has seen at the club.

"To be honest, I haven't (seen) a player as quick as Aubameyang before, even though we have Jakub Blaszczykowski who is very pacy as well," Bender said.

"But Aubameyang tops it. Henrikh Mkhitaryan is also a very quick and flexible player, Robert Lewandowski and I forgot Marco Reus as well, they all are very quick and as far as I know, it's the quickest attack I have ever played with."

But Bender acknowledged Dortmund need to shore up their defence in the coming Bundesliga campaign.

After conceding just 47 goals in both their title-winning seasons of 2010/11 and 2011/12 combined, Juergen Klopp's men leaked 42 goals last-season alone - something Bender is determined to rectify.

"We didn't want to concede 42 goals when we started last year, that's what caused us a lot of trouble," Bender said.

"In the past few years it was our strong defence helping us to be successful.

"That's the most important thing in football, you try to avoid conceding goals so that you don't need to score more to win matches. That's where we need to improve."