Sehorn, who's coming back from knee surgery, has been playing nickel back, and has relinquished his starting role from 2001.
Wednesday marked the first time he's practiced as a starting corner this year, which makes Brown the likely starter in place of Peterson.
Brown played most of the game in Dallas last week.
"I'm not worried about Ralph," head coach Jim Fassel said. "He wasn't beaten. He blew the coverage [in Dallas]. There's a difference. No one talks about him doing his job on 66 other plays. He was close to getting interceptions a couple of times."