Wary of sacks, bad backs and the flu, the Washington Redskins churned through another practice of change and substitution yesterday afternoon at Redskin Park.

Coach Joe Gibbs, figuring that two all-pros playing out of position might be better than one first-year player playing in the right spot, has decided that left guard Russ Grimm will start in place of Dan McQuaid at left tackle against the New York Giants (7-3) Monday at 9 p.m. at RFK Stadium.

Center Jeff Bostic will replace Grimm in a reunion of the line that yielded seven sacks in a 17-3 loss to the Giants last month.

But it's also a line that gives the Redskins (5-5) a more experienced player opposite Giants defensive end Leonard Marshall, the league leader in sacks with 12 1/2.

While the Hogs appear set for this week, two other high-profile Redskins are ailing: right defensive end Dexter Manley has the flu and running back John Riggins a stiff back.

Manley spent his second consecutive day in bed with a fever and nausea. Gibbs said the Redskins were sending a doctor to his house last night to examine him -- and are keeping their fingers crossed.

"We think it's just the flu," Gibbs said. "Dexter's been playing good football for us. We need him out there. Hopefully, this is something like 48 hours and he'll be fine."

Veteran Tom Beasley and first-year player Steve Hamilton worked in Manley's place.

Manley's wife, Glinda, said yesterday that her husband wants to practice today, but didn't sound overly positive about his plans.

"He's sweating, has a fever, everything," she said. "He's been in bed sleeping all day.

"Now I've caught it, too, so we're both wearing masks around the house so the baby (nine-month-old Dexter Keith II) doesn't catch it."

Riggins took the day off after developing stiffness in his back yesterday morning. The Redskins immediately added him to their injury list (he is probable for the Giants), but Gibbs said Riggins isn't expected to miss any more practice time.

Then again, no one knows for sure until the 36-year-old running back rolls out of bed each morning.

"We plan on starting John unless he misses again (today) and he doesn't feel good," Gibbs said.

While Riggins watched practice in a blue warmup suit, George Rogers worked as the starting running back.

Riggins, who had problems in his lower back and hip last season, bruised the middle part of his back in a game against the Cleveland Browns Oct. 27 and missed the Atlanta game the next week.

He came back to start against Dallas last Sunday but gained just 34 yards in seven carries as the Redskins lost, 13-7.

In previous weeks, Riggins has missed the first practice of the week, then returned later on. This time, he worked out Thursday and "looked real good," Gibbs said, then developed the stiffness.

Gibbs said he is not concerned that the stiffness apparently resulted from practice this time, not a game.

Strong safety Tony Peters (groin pull) also missed practice, but expects to return today.

"It's one of those things with a defensive back, you want to be careful," Peters said. "We'll see how I feel. I'm still a little sore."

Peters was injured late in the Dallas game. Rookie free safety Raphel Cherry and veteran safety Greg Williams have been practicing in his place.

Middle linebacker Neal Olkewicz (torn right pectoral muscle) went through noncontact drills yesterday and is expected to play Monday.

Rich Milot would move from right linebacker to the middle if Olkewicz couldn't play.

So, if all goes well for the Redskins, the change on the offensive line will be the only move of the week.

Earlier in the week, the Redskins appeared ready to stick with McQuaid, who gave up five sacks to Dallas' Jim Jeffcoat. "We'll start the other way (Grimm and Bostic) and just see how we go," Gibbs said. "Both (McQuaid and Grimm) will see a lot of work."

More than likely, the thought of Marshall, who had 1 1/2 sacks against the Redskins the last time, was enough to force Gibbs to go with experience.

"He is one of, if not the best, defensive linemen in the league," Gibbs said. "That's been our luck lately."

Marshall, who had his first sack since the Redskins' game last Sunday against the Los Angeles Rams, knew all about Jeffcoat's performance last week.

"I'm dying to get at those films," Marshall told New York reporters.

Now, he gets the same lineup he saw in October -- or does he?

Grimm and Bostic played that game under strange circumstances. All-pro left tackle Joe Jacoby was supposed to start, but, in pregame drills, realized he couldn't push off on his sprained right knee. (That's the same injury that has forced him to miss three more games and will keep him out Monday.)

So, Grimm had to move to tackle, leaving the guard position open. Bostic was chosen to fill in there, even though he had come off injured reserve just the day before. It was his first game in a year after reconstructive knee surgery, and he was playing at a different position.

This is no rush job now. By game time, Grimm and Bostic, who has not started since the Giants game, will have had four practices to work at their new positions -- and to work together.