"We're having a bit of a flu wave so we'll have to wait and see," Sahin told a press conference on Wednesday.
Sixth-placed Dortmund's defence will also be without Niklas Sule due to injury and midfielder Pascal Gross is suspended after he was sent off during last month's 3-1 win over VfL Wolfsburg.
Sahin said playing champions Leverkusen, who are unbeaten in the league since August, would be difficult.
"(Coach) Xabi Alonso has changed everything at Leverkusen. He has stabilised them and added more and more. They're exceptionally good. It's a team that has a lot of control in the game, but we want that too," Sahin said.
Dortmund are unbeaten in their last five matches, including a draw with leaders Bayern Munich in November, as they look to close a two-point gap on the top four in a bid to qualify for the Champions League.
"A win would be extremely important for the table. We're playing against a top opponent. We've always performed well against these teams so far. We want to get into a flow for the new year with a good game," Sahin added.