Under normal circumstances, merely putting on a helmet and pads and grinding through a two-hour practice would be routine for linebacker Mike Barrow, a veteran of 11 NFL seasons and one of the Washington Redskins' key offseason acquisitions. But after more than three weeks of sitting on the sideline wearing shorts and a visor, Barrow's arrival on the field in the tools of his trade drew considerable attention yesterday.

His appearance, however, was misleading. Barrow only wore pads during individual drills and did not participate in a full practice due to a tendon strain in his left knee. The linebacker, a tackling machine who was signed in the offseason to strengthen the middle of the defense, does not expect to play Friday in St. Louis -- fellow linebacker LaVar Arrington is expected to miss that game as well -- and is unsure if he will be ready to play by the start of the regular season Sept. 12.

"I'm just taking it one day at a time," Barrow said. "I don't know what's going to happen. I never missed this many games in my career -- well, I take that back. I did miss three games [in one season] -- so I'm at my max right now. I'm a little frustrated about that."

Barrow, 34, started all 16 games for the New York Giants last season and set a career high with 150 tackles, the second highest total in franchise history. He led the Giants in tackles for three straight seasons and played for Carolina and Houston previously; Houston drafted him 47th overall in 1993. Gregg Williams, Washington's assistant head coach-defense, was with the Oilers when they selected Barrow from the University of Miami, which pumps out sturdy linebackers annually, and he signed a six-year deal with the Redskins in April.

The knee injury occurred during passing camp last month, a few days before players officially reported, and Barrow aggravated the problem during a practice on Aug. 7. He can run well, but experiences pain when he tries to cut or stop, and he tweaked the injury again Monday, which left him unable to practice fully yesterday.

Barrow is receiving daily treatment from the training staff, and has seen various specialists for second opinions on the injury, which he said was originally considered tendinitis. He has continued to get treatment on his own as well as outside of Redskins Park, he said, and is trying to work back onto the field without experiencing another setback.

"I'm doing everything I can within my knowledge to get back on that field -- everything," said Barrow, who has missed just five games in his career and two in the last eight seasons. "We're just taking it easy and waiting on my tendon to heal. It's no set timetable. I'm just going as I go and we keep pushing it a little bit every day and seeing what we can do and if I irritate it then we just back on down."

Arrington also remained out with a strain in his left knee and has been off the field for a week. Arrington is nearing a return, Coach Joe Gibbs said, and while he may still be held out of Friday's game, he could return to practice this week. "He told me today he's anxious to get back out there," Gibbs said. "So I think he's getting closer."

Like Arrington, Barrow was limited to agility drills yesterday. Although Barrow has been in every meeting and has a good grasp of the defensive system, his lack of on-the-field training and contact is a major factor. Preparing to play mentally and physically are vastly different.

"The thing you're always more concerned about there is conditioning, game conditioning," Gibbs said. "That's why you hate for guys to miss camp, because there's a certain amount of conditioning to having pads on and hitting people, and if you're not then you worry about that, how long can they go in the opening game."

Barrow concurred: "It's the difference between understanding what to do when you're sitting down in the AC in a room sipping on some Gatorade. And it's another thing when you're playing in the hot sun and you're sipping on some Gatorade and needing more Gatorade. So one is definitely better than the other. . . .

"I try to stand behind the [linebacker] unit [during practice], and make the steps like I would on the field and make the calls like I would on the field, but still, you've got to be in the fire to experience what's going on."

Linebackers bear a heavy responsibility in Williams's system -- they are the quarterbacks on the defense. Barrow's intellect is one of his strengths -- he is able to read the offense and help align his teammates -- but there has been little time to build chemistry among the linebackers. The coaches have yet to see their three starters -- Arrington, Barrow and Marcus Washington -- in a game at the same time, and that may not occur in the preseason. So they continue to work with reserves such as Antonio Pierce, who is having a fine preseason.

"It's like war," linebackers coach Dale Lindsey said. "If you have attrition, you've got to get the next group in there and get them ready to fight."

A rare sight for the Redskins -- Mike Barrow participating in a full practice. Barrow, a key offseason acquisition, has a tendon injury and is unsure if he will be ready for the season opener on Sept. 12.