"I haven't made that decision," Shanahan said Sunday. "We'll see what happens during the week with our football team and obviously share with the players first."
Shanahan said he was pleased with the decision-making of Beck, whom the Colts sacked three times Friday in Washington's second preseason game.
"Good quarterback play is taking a sack when you have to take a sack, trying to make something happen when you're able to make something happen," said Shanahan, who attributed Beck's lack of downfield passing to the Colts' zone defense. "And I thought John made some good decisions."
Beck started the game and completed 14 of 17 passes for 140 yards. Grossman threw for 88 yards on 8-of-12 passing in relief.
In the Redskins' preseason opener, Grossman completed 19 of 26 passes for 207 yards with a touchdown on Aug. 12 against the Steelers -- a game Beck missed after he injured a groin injury in practice.
With his stellar play against the Colts in his preseason debut, Beck held serve in the quarterback competition.
"He's a gamer," wide receiver Jabar Gaffney said. "From everything we do in practice, he was a totally different guy out there on the field in the game.
"His energy level picked up. It picked up a lot. That surprised me a little bit, but I'd say it's a good thing."
After practice on Friday, Beck was surrounded by a media swarm, causing a few teammates to shout cautionary words. "Don't kill the guy, man." "Let the man breath." "Don't kill the man."
The scrutiny will be strong until Shanahan picks a starting quarterback.
"They know what they're doing in this offense, both smart and savvy guys," tight end Fred Davis said. "And John went in and did what he had to do, too. I'm just glad I don't have to make that decision."
The Achilles' heel injury that kept S LaRon Landry on the physically-unable-to-perform list has healed, but he tweaked his hamstring working out in Indianapolis. His status is day-to-day, and he remains on the PUP list. S Oshiomogho Atogwe participated in every portion of practice, but he's still working his way back to full speed. ... DE Adam Carriker, who missed the Colts game because of blisters on his foot, didn't participate in drills while media watched practice. Wearing socks and sandals, Carriker rode a stationary bike during team stretching and stood to the side watching defensive-line drills. WR Brandon Banks is receiving platelet-rich plasma therapy for his injured knee. He'll miss Thursday's game, but Shanahan hopes he can play in Washington's final preseason game against the Buccaneers on Sept. 1. LB Edgar Jones, who sustained a concussion while covering punts against the Colts, said the headaches he was experiencing Saturday have subsided, but he's still sensitive to light. ... LB London Fletcher sat out against the Colts with a groin injury, but could he have played? "I don't know. Next question." He participated in every portion of practice, but he didn't play at full speed. Shanahan hopes WR Malcolm Kelly, who has been out with a foot injury, will practice within a week. WR Terrence Austin hasn't returned a regular-season punt in the NFL, but he's returned a team-high five this preseason and is averaging 12.8 yards per return. ... After cutting K Shayne Graham on Aug. 14, Washington signed Clint Stitser on Thursday to compete with Graham Gano. Stitser made 7 of 8 field goals and 8 of 10 extra points for the Cincinnati Bengals last year. He wore a nameless No. 3 jersey Sunday. The Redskins ended practice early due to lightning. Three defensive plays and a 10-minute special teams period remained when the team headed indoors.