"In terms of experience and proven depth, wide receiver may be the one position where the Rams can least afford a significant injury. So the news that wide receiver Donnie Avery could miss four to six weeks with a foot injury is a blow to the team's early season offensive hopes.

"The MRI showed more than we thought," coach Steve Spagnuolo said through a team spokesman after Sunday afternoon's special teams workout. "It's probably a four- to six-week injury."

Sources told the Post-Dispatch that Avery has suffered a stress fracture in his left foot. Such injuries often require nothing more than time to heal. Even under the four- to six-week outlook, Avery would be sidelined the entire exhibition season at a minimum. If he's out six weeks, he could miss the first two regular season games (Seattle Sept. 13 and Washington Sept. 20).

But stress fractures can be tricky. It's not unusual for them to take longer to heal than expected. During Sunday morning's practice, Laurent Robinson and Keenan Burton worked with the starting unit. Tim Carter, who was one of the more productive receivers in Friday's scrimmage at Lindenwood University, also got some reps with the first unit.

Derek Stanley, Ronald Curry and rookie Brooks Foster also could be in the mix, beginning with this Friday's preseason opener in the Meadowlands against the New York Jets.

"Any time anybody goes down, you have to step your level of play up," Burton said. "That's from top to bottom. From the rookies, all the way up to Carter and Curry having seven years (experience). So you've got to go out and play."

Burton added: "I don't necessarily know how (Avery's injury) affects me at all. I'm going to play my position. I know all the receivers are going to play their positions. And we're going to go out here and compete."

The Rams worked out two free agents Sunday: defensive end Shaun Smith (most recently with Cleveland) and safety Anthony Scirrotto (most recently with Carolina). But no wide receivers. That could change this week.

By all accounts, the team didn't know the severity of Avery's injury until Sunday afternoon. Avery suffered the injury in Friday's scrimmage, although it's not clear when it happened, or even if it happened on a specific play.

During his regular media briefing after Sunday morning's practice, Spagnuolo said Avery felt some discomfort in his left foot when he woke up Saturday — the morning after the scrimmage.

"(Trainers) worked on it a little bit, they X-rayed it — didn't find anything," Spagnuolo said. "We thought he'd be able to go today, but it still felt a little bit tender.""