The winger has scored 16 league goals and made 13 assists this term and been tipped to surpass that tally in 2014/15
The Poland international finished the season as the Bundesliga's top scorer with 20 goals and will leave the North Rhine-Westphalia club to join their rivals and league champions Bayern Munich.
However, Klopp isn't worried about the loss of the 25-year-old striker, insisting Reus, who scored 16 league goals and set up a further 13 from the wings, can take over the responsibility as the side's main scorer.
"Next season it's Marco Reus' turn to finish as Bundesliga top scorer," the coach told reporters after the 4-0 win over Hertha on Saturday.
Reus picked up an injury during Saturday's match, limping off as he was replaced by Pierre-Emerick Aubameyang, however the club revealed on their website the 24-year-old isn't expected to miss the DFB-Pokal final against Bayern next Sunday.
During the meeting with Hertha, Lewandowski netted twice in his final league game in a Dortmund shirt, scoring a neat free-kick to wave goodbye to the BVB faithful, and Klopp joked that it was one of the very few dead balls he has seen him score.
"He practiced free kicks for four years. From doing 8000 in training no more than three went in - unfortunately this is the truth."
The 46-year-old then spoke of his happiness after ending the season with a win.
"I am extremely satisfied, we have deserved it and pretty much won because we were highly motivated to get to 71 points."