Smoot took a hit to the head from safety Matt Bowen as the two defended Rob Johnson's pass to Cliff Russell. Trainer Dean Kleinschmidt said Smoot was unconscious for "less than a minute" and woke up with a headache and back pain before being placed on a board and loaded in an ambulance.
"He had feeling," Kleinschmidt said. "He could move his arms and legs and feel and squeeze. He responded. He did not have amnesia."
Kleinschmidt said Smoot probably would be diagnosed with a concussion, pending tests at the hospital.
Practice was stopped for about five minutes as Smoot was treated.
"When I saw him on the ground, and he just wasn't moving, that was the scary part," cornerback Champ Bailey said. "He was going in and out a little bit, but once they took his facemask off and they just had him lying on his back, he looked like he was at least aware of what was going on. I looked at him and he kind of smiled a little bit, so that was a good sign."
Bowen's aggressiveness in practice has been a problem for the Redskins since the start of training camp. He leveled running back Trung Canidate during the first week of practice, drawing the ire of coaches and cheers from his fellow defensive players.
Coach Steve Spurrier did not blame Bowen directly for Smoot's injury, but the coach said: "We've all got to realize we're practicing against each other."
Bowen, who was not hurt on the play, declined to speak to reporters.
Smoot's availability for Sunday's game against the New York Giants is in question, which would be a significant setback for the Redskins. He and Bailey are one of the top tandems in the league, and backup Rashad Bauman pulled his hamstring in last week's game against the Atlanta Falcons.
"With a guy like that, you lose a lot. You lose his talent. You lose his energy," Bailey said. "You can't replace Fred. ... He's one of a kind. It's definitely going to hurt this team."
Bauman, a second-year player, will start if he is healthy and Smoot isn't. Next in line would be undrafted rookie Ade Jimoh, who allowed a late touchdown filling in as the nickel back Sunday against Atlanta.
Bauman said his hamstring is sore, but he participated in the full practice. He said he's ready for what would be his first NFL start.
"You don't want it this way, but hopefully Fred will be good," Bauman said.
Smoot was a second-round draft pick from Mississippi State in 2001. He's one of the team's most jocular and talkative players, so Bauman wasn't sure at first whether Smoot was really injured.
"I thought Fred was joking," Bauman said. "Fred is a comedian. But as it continued, he stayed on the ground, it just got worse and worse."