Coach Dick Jauron listed Losman as day to day, saying the quarterback's right thumb was too swollen for him to practice. Losman's thumb was heavily wrapped as he watched practice at Bills training camp facility in suburban Rochester.
He was hurt following through on a pass attempt, when his thumb struck a teammate's helmet during the Bills' first practice in full pads Monday. The second of Buffalo's two 2004 first-round picks, Losman lost his starting job to 2007 third-round pick Trent Edwards last season.
Also on Tuesday night, starting free safety Ko Simpson missed the final hour of the two-hour session after jamming his left ankle in the artificial turf.
Jauron said the injury isn't considered serious, adding that trainers held Simpson out as a precaution. The injury was to the same ankle the player broke in the Bills' season opener last year, forcing Simpson to spend the rest of the campaign on injured reserve.
Starting outside linebacker Angelo Crowell was held out of practice as a precaution after experiencing soreness in his left knee.