Ken Dorsey was among the last players off the San Francisco 49ers' practice field Wednesday, a bag of footballs slung over his sweaty shoulder following his usual post-practice throwing session. Even though Dorsey probably will start for the 49ers on Sunday in place of injured rookie Alex Smith, the recent third-string quarterback is sticking to his routine of extra work and additional preparation. Smith, the No. 1 overall draft pick, has two strained ligaments in his right knee -- and Tim Rattay, the early season starter and recent backup, will be on the opposite sideline as a backup for the Tampa Bay Buccaneers, who acquired him in a trade last week.