Dorsey injured his left arm at practice Friday and left the field after being attended to by the training stuff. He will have surgery Monday.
Dorsey was hurt on his 29th birthday. He is set to be a free agent after this season.
Dorsey came into his own when he signed with the 49ers and was an instant success at nose tackle. Dorsey didn't make much of a difference in five seasons with the Kansas City Chiefs. Kansas City took him with the No. 5 overall pick in 2008.
Second-year player Quinton Dial, a fifth-round pick out of Alabama last year, should get reps with the first team in Dorsey's place. Dial is having a productive camp.
The 49ers also have Ian Williams, who was the starter at the beginning of last season. He suffered a severe leg injury in Week 2 at Seattle and was lost for the year. He is still not practicing, but the team is hopeful he can play this season.
ESPN.com 49ers reporter Bill Williamson contributed to this report.