John Mensah has earned high praise from his Sunderland central defence partner Michael Turner who says the Ghanaian is the best defender he has played alongside.Despite spending a lot of time out injured, Mensah has been impressive for Sunderland when he has played including in the last two games during which he has been the outstanding performer.Now Turner feels his fitness could prove crucial to Sunderland's efforts to avoid relegation.Turner hailed the Ghanaian for bringing quality to a back-four which has tightened up considerably since conceding seven goals at Stamford Bridge in January.Asked if he had played alongside a better defender than Mensah, Turner replied: "No, probably not. Unfortunately for him and for us he's not managed to stay fit for a run of games which is disappointing."He is a top drawer, world class player who we'd like to have fit. He has a lot of great attributes. He is very strong, quick and a calming influence on the ball. He is just a top quality defender."Source: Kickoff.com