Borussia Dortmund defenders Waldemar Anton and Almugera Kabar are doubtful for Friday's Bundesliga game against Bayer Leverkusen after a virus struck the team's camp.

"We're having a bit of a flu wave so we'll have to wait and see," Dortmund head coach Nuri Sahin said at a pre-match press conference on Wednesday.

Sixth-placed Dortmund will also be without Niklas Sule due to injury, while midfielder Pascal Gross is suspended after he was sent off during last month's 3-1 win over Wolfsburg.

Sahin said playing champions Leverkusen, who are unbeaten in the league since August, would make for a difficult return to Bundesliga action.

"Xabi Alonso has changed everything at Leverkusen. He has stabilised them and added more and more," Sahin said.

"They're exceptionally good. It's a team that has a lot of control in the game, but we want that too."

Alonso is, however, winless against Dortmund as a coach, recording two draws and one defeat against them.

Against no other club has the Spaniard been in the Bayer dugout for as many matches without winning one.

Dortmund, meanwhile, 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 to the top four.

BVB are also unbeaten in their last 11 home Bundesliga matches (eight wins, three draws), though Leverkusen – unbeaten in 24 on their travels (18 wins, six draws) – could set a new club record for successive Bundesliga road trips without a loss.

"A win would be extremely important for the table. We're playing against a top opponent," Sahin said.

"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."