"Ultra-competitive," coach Brad Childress said of Walker. "He ran very well and worked out very well for us here this morning."
The 29-year-old Walker played in 14 games last season for the Baltimore Ravens, but he went unsigned until this week. He said the Vikings were the fifth team he's worked out for this fall.
"Some situations my agent didn't like, so he just told me to hold on," Walker said. "He liked this one."
Rookie cornerback Chris Cook's status is also in question this week because of a left knee injury, though he was a limited participant in Wednesday's practice.
Cook missed Monday's game after surgery to repair a torn meniscus. He was hurt against the Detroit Lions on Sept. 26, but he didn't realize it until well into the team's bye week and an MRI revealed the tear.
"I was just hoping it was like a bruise or something from the game, but I got the MRI and it told the true story," Cook said.
He said he's pushing to be ready to play on Sunday against the Dallas Cowboys, particularly with Griffin gone.
After trading backup Benny Sapp in the preseason, the Vikings are short on healthy bodies at a critical spot. Allen and Sheppard are the only other available cornerbacks after veteran Antoine Winfield. Marcus Sherels was signed to the practice squad.
Center John Sullivan also sat out Wednesday's practice because of his lingering calf injury. Tight end Visanthe Shiancoe was limited with his hamstring injury. Backup defensive end Brian Robison was limited because of an ankle he sprained against the Jets.
Wide receiver Sidney Rice, on the physically unable to perform list following hip surgery in late August, said Wednesday he's gotten rid of his crutches and that he's "feeling pretty good" in his rehabilitation. He met with his doctor in Colorado on Monday.
Though Rice said he's unsure exactly when he can begin resuming running and other football-related activities, he was adamant that he won't need to be placed on injured reserve. Asked whether the addition of Randy Moss allows him more time to recover, Rice said no.
"That means when I do get back, then teams are going to have some trouble," Rice said.