The Poland international was widely expected to join rival Bayern Munich ahead of the 2013-14 campaign, until Dortmund vetoed a move to the Champions League winner. Much has since been said about the 24-year-old's future, but Kehl has stressed that the chapter has now been closed at last.
"Robert Lewandowski's situation is no longer an issue," Kehl was quoted as saying by Bild. "He has already said last year that he will deal with the situation like a professional. He will give his all for Borussia Dortmund."
Kehl then went on to discuss Mario Gotze's transfer to Bayern Munich and stated that the attacking midfielder would have been better off staying at BVB for at least one more season.
"I believe that Dortmund and Bayern have grown closer together in the past few years from a sporting point of view. It would not have hurt Mario to stay put for one or two more seasons.
"Of course, it hurt a lot when I heard about his decision. It took me by complete surprise.
"The transfer gives us a lot of opportunities, though, and we will have to make use of it in a creative way. The team remains stable and will not be worse than last year. I even think that we will be better."
Dortmund has recently been linked with Henrik Mkhitaryan, Christian Eriksen and Kevin De Bruyne in their search for a replacement for Gotze.