The BVB trainer is pleased with the influential midfielder's return to form, and has warned his team that Freiburg will pose a stern test on Saturday
Sahin re-joined his boyhood club this winter after unsuccessful spells with Real Madrid and Liverpool, and has since made seven league appearances for BVB.
"Nuri’s getting better and better," Klopp was quoted as saying on the official Bundesliga website.
"Our second half against Schalke was better mainly because Nuri was playing. He has taken a big leap forwards."
Klopp then went on to discuss Dortmund's Bundesliga match against Freiburg, and stressed that BVB cannot afford to underestimate their opponents.
"They’ve had an unimaginably good season. If we give it anything less than 100 per cent, then that will not do.
"They have fantastic individual quality, but we’ve got to live with it and find solutions which our opponents won’t expect."
Saturday's encounter is scheduled to kick off at 15:30CET.