Bayern Munich winger Arjen Robben will undergo knee surgery and is expected to be out for around four weeks, the Bundesliga club said on Thursday. Robben was forced out of Bayern's goalless draw with Juventus in the Champions League, only playing for 45 minutes at the Allianz Arena. Scans proved that the injury-prone Dutchman has an irritation of the plica tissue in the knee joint, which requires a knee operation soon. "The cartilage and ligaments are OK," said coach Louis van Gaal. "We are fortunate also that we have a break next week for internationals." French winger Franck Ribery is also doubtful for the weekend's league game with Cologne, so is center-half Daniel van Buyten.
