J.J. Stokes, San Francisco's top draft choice and an All-American wide receiver at UCLA, broke a bone in his right hand in a noncontact drill at the 49ers' training camp in Rocklin, Calif., Thursday.
Stokes' hand will be in a cast at least four weeks, and he could resume playing in five or six weeks. That would put him out until the fourth or fifth game of the season.
He is the second 49er to be injured in two days, joining fullback William Floyd, who sprained right knee ligaments Wednesday and will sit out about three weeks.
Free agent defensive back Toi Cook agreed to contract terms. He will join the team Sunday.
Cook will be paid the veteran minimum of $178,000 with a chance for bonuses.