DENVER -- Oft-injured running back Terrell Davis underwent arthroscopic surgery Thursday to relieve swelling in his right knee, a procedure that could sideline him for up to six weeks.

	Davis

Denver Broncos coach Mike Shanahan said doctors termed the surgery successful after removing some debris and repairing a small cartilage tear.

"It will take two to three weeks for him to recover and four to six weeks before he's able to play," Shanahan said Thursday.

"You always hate to lose a great player. Common sense says every time you go in there and have to do surgery, the chances are a little less likely you can come back as you were. Hopefully, Terrell will be able to come back and help this football team before the season is over."

Earlier Thursday, the Broncos downgraded Davis from probable to definitely out on their injury report for the game Sunday night (ESPN, 8 p.m. ET) in Arizona. Davis was not at practice Thursday.

Shanahan on Friday denied a published report that said Davis also partially tore his medial collateral ligament.

"No, no ligament damage," he said. "Only cartilage."

He said Thursday's arthroscopic procedure was similar to what linebacker John Mobley underwent during training camp last season. Mobley also tore his anterior cruciate ligament and experienced swelling a year later. After the second operation, Mobley missed only three weeks.

"Terrell's was similar but not as bad," Shanahan said.

It is the same knee Davis tore his ACL in 1999. That injury, coupled with a stress reaction in his lower left leg the following year, caused Davis to miss 24 of 33 games during the 1999 and 2000 seasons.

Mike Anderson, who inherits the starting job, said Davis informed him of the impending surgery Wednesday.

"Terrell told me himself after practice what was about to take place," Anderson said Thursday. "He was letting me know before anybody else did, so I could get ready. It kind of came as a shocker.

"He was pretty bummed out about it. But he looked at it as something that he had to do. He has to find out what's going on in his leg. He had been putting it off, I guess, since training camp. He wasn't feeling right. His knee was all swollen."

When Davis and Olandis Gary went down with injuries early last season, Anderson, a rookie drafted in the sixth round, stepped in and rushed for 1,487 yards, earning the NFL Offensive Rookie of the Year award.

"This kind of reminds me of last year," Anderson said. "A similar thing happened, and I had to be ready at a moment's notice. I've been preparing myself all the way through training camp and in our first game, and now it's up to me.

"I'm hoping to go out there and just pick up from where I left off."

Davis, the NFL MVP in 1998 after rushing for 2,008 yards, had a setback in his right knee during training camp. At the time, the Broncos described the condition of his knee as "degenerative."

He started the regular-season opener against the New York Giants, rushing for 101 yards on 21 carries. But he had to have his knee drained twice in the past two weeks.

At his weekly news conference Wednesday, Davis made no mention of his most recent knee problem.

Anderson said he wasn't assuming he would necessarily be the starter for the next month or so.

"I don't know how this thing will play out," he said. "As of right now, I'm just looking at this game and this game only. Then I'll come back next week and go from there. I don't know how long Terrell is going to be out.

With Anderson and Gary now running 1-2, Shanahan said there were no immediate plans to add a running back to the roster.