SANTA CLARA Wednesday's 49ers practice landed linebacker Patrick Willis in a cast. Thursday's knocked cornerback Chris Culliver out for the season.
The team's No. 3 cornerback was covering a punt early in the training-camp session when he switched directions, fell to the ground in a heap and immediately clutched his left knee. Culliver was carted into the team's training room and then taken to Stanford Hospital for an MRI that revealed a torn ACL.
Willis, meanwhile, was at the same hospital earlier Thursday. He suffered a fractured right hand during a pass-rush drill Wednesday, the fourth time he has broken a bone in that hand since he was a junior at Ole Miss.
No Super Bowl loser has won a championship the following season since the 1972 Miami Dolphins, and the 49ers must feel as if the Super Bowl loser's curse is fixed squarely upon them right now.
The team already lost starting wide receiver Michael Crabtree for most of the season when he tore his Achilles' tendon in May. On Thursday, they went through practice with four starters Willis, NaVorro Bowman, Aldon Smith and Jonathan Goodwin on the sideline. In all, 16 players on the 90-man roster were absent.
"Well, there's been some nicks, and you try to dodge bullets," coach Jim Harbaugh said. "Sometimes you don't dodge them all."
The ever-positive Harbaugh, however, noted the silver lining from all the injuries: Backups and lesser-known players will get a chance to prove their worth.
Culliver played 63 percent of the defensive snaps last season. Among the cornerbacks who will get more attention with him out is Nnamdi Asomugha.
Asomugha, 32, has stood out the past two practices. He had an interception Wednesday and also managed to do something few 49ers defenders have done this offseason break up a pass from quarterback Colin Kaepernick to wide receiver Anquan Boldin. He had another notable pass breakup Thursday.
"He did have noticeable, eye-popping plays, (Wednesday) especially," Harbaugh said. "He's been good. I think he's got a good grasp of what we're doing, defensively. In shape, doing a nice job."
Other backups at the position include Tramaine Brock, who filled in as the No. 3 cornerback Thursday, and Perrish Cox, who intercepted a pass by backup quarterback Colt McCoy during 11-on-11 drills.
The player who will fill in for Willis at linebacker is Michael Wilhoite, who made a splash on special teams when he was elevated from the practice squad late last season.
Wilhoite played safety at Washburn University. That gives him a good background for Willis' so-called "Jack" linebacker position, which requires him to cover tight ends and running backs down field. Wilhoite said Willis already had been serving as a mentor, and that role probably will increase now that he's on the sideline.
"A lot of times, a coach can only say something in so many ways and it still goes over your head and you don't understand it," Wilhoite said. "But with (Willis) he's been doing it for so long. He's taught it, he's learned it, he's played it and he's played it the best anybody's ever played it. It's easy to learn coming from him."
Willis is unlikely to play in the exhibition season, which begins Thursday. But Harbaugh said the inside linebacker, who led the NFL in tackles in 2007 despite a broken hand, would not miss the Sept. 8 regular-season opener against Green Bay.
"I expect him to be back, and it won't be something that keeps him out very long," Harbaugh said.