It is "doubtful" Washington Redskins strong safety Ken Coffey, who underwent knee surgery today, will play this season, head trainer Bubba Tyer said.

Coffey was injured in the third quarter of the Redskins' 17-14 preseason victory over the Falcons in Atlanta Saturday night. He will be in a cast six weeks, then will begin rehabilitation, Tyer said.

Dr. Stan Lavine, the team physician, repaired two torn ligaments -- the anterior cruciate and the medial collateral -- and repaired the medial miniscus cartilage in Coffey's knee in surgery at Sibley Hospital.

"It's the most disappointing thing that's happened to us," Coach Joe Gibbs said.

This is the third time in Coffey's four-year career that he has suffered a serious injury or illness. As a rookie in 1982, he spent the season on injured reserve with a blood disorder. In 1984, he missed four games because of a shoulder separation incurred in training camp.

The Redskins made changes in their secondary today to compensate for Coffey's loss. Former all-pro Tony Peters has been moved to the first team, as expected.

Rookie cornerback Barry Wilburn, who has been impressive in training camp, will work both as a nickel back and strong safety, assistant coach Richie Petitbon said.

"We want to get Barry acclimated to strong safety," Petitbon said. "By no means are we giving up on him at corner. We think he'll be a good corner for us. But this is something we have to do."

Wilburn played two years of free safety at Mississippi and said he also worked at strong safety in college practices and in the Redskins' May minicamp.

Reserve free safety Greg Williams also will receive work at strong safety, Petitbon said.

The Redskins plan to keep rookie free safety Raphel Cherry at strong safety. Depth is a problem there, too, with the loss of waived veteran Mark Murphy.

Defensive tackle Dave Butz practiced for the first time and joined the first team in drills.

"Dave Butz, Dave Butz," cornerback Darrell Green yelled as he ran into a huddle. "High five, high five."

With that, Green jumped -- Butz didn't -- and they slapped palms.

"The biggest thing getting used to is the pads and the double-knee braces," Butz said after practice. "The pads are very restricting."

After a grueling, two-hour practice in 90-degree heat, he said, "I can't keep up with them (the other players) wind-wise, but I think I can strength-wise."

Butz agreed to a $975,000, two-year deal last week after a two-week holdout. "All the pressure is on me right now," he said.

Why did he hold out? "I'm probably one of the best (defensive tackles) and I'm trying to get better."