Bayer 04 Leverkusen midfielder Tranquillo Barnetta could miss the entire UEFA Champions League group stage as he requires further knee surgery.

The Swiss international went under the knife in January and returned for the final seven Bundesliga games in March. Problems in his right knee resurfaced during pre-season training, however, and the 26-year-old will undergo another operation on Monday.

Barnetta is now expected to be absent until the new year, meaning he will sit out Leverkusen's UEFA Champions League Group E campaign against Chelsea FC, Valencia CF and KRC Genk. He will also miss Switzerland's three remaining UEFA EURO 2012 qualifiers, with Ottmar Hitzfeld's side sitting third in Group G and next up against Bulgaria on 6 September.