Bundesliga leaders Bayer Leverkusen have lost the services of captain Simon Rolfes for up to three weeks following knee surgery,
Rolfes will definitely miss the visit of Borussia Dortmund and the trip to Schalke following surgery to clear out a knee joint which was also operated on during the close season.
The defensive midfielder went under the knife to cure a problem with his meniscus in June.
"It wasn't a complete surprise but it's still a bitter blow," said coach Jupp Heynckes.
"But the player's health definitely comes first so it was important to have the operation now.
"There are several options and I've got full confidence in these players."