PARIS, Feb 15 (Reuters) - Stade Rennes' hopes of clinching a Champions League playoff spot took a major blow on Friday when they lost 2-0 at Lille and midfielder Romain Alessandrini suffered a possible serious knee injury. Lille prevailed thanks to a Chris Mavinga own goal and a Dimitri Payet header either side of the interval to move up to eighth in France's Ligue 1 with 37 points from 25 games. Rennes were eyeing third spot but stayed fifth on 40 points, 11 behind leaders Paris St Germain who travel to Sochaux on Sunday.