The concussion Trent Green suffered on Sunday was diagnosed as grade three, the most severe, and he'll undergo further tests to determine his future. He has been ruled out of Sunday's game at Cleveland, and Cameron declined to discuss the possibility the injury will force the 37-year-old Green to retire. "I don't think we really know the full extent, because there are some ongoing tests," Cameron said. "Right now I just think there are too many unknowns." Cleo Lemon, who replaced Green at Houston, will make his second NFL start against the Browns. Second-round draft pick John Beck becomes the backup. The loss of Green is another blow in a season where little has gone right for the winless Dolphins and their first-year coach.