Walker is the Broncos' top pass-catcher, with 19 receptions for 230 yards in three games this season, although he has no touchdowns.

Coach Mike Shanahan said in on the team's Web site the procedure was to "clean out" the knee.

"The doctor that operated on him estimated six weeks, so we'll get a better feel probably in the next week or so,” Shanahan said.

Walker's replacement, Brandon Stokley, starts his third straight game Sunday when the Broncos face Pittsburgh.

"I feel good," the nine-year veteran said. "The last two weeks he hasn't been in there and I felt good. Just go in there and make some plays and that's it, really."

Stokley joined the Broncos after six seasons with defending Super Bowl champion Indianapolis.

He has 12 catches for 178 yards in five games.