He confirmed on Monday that Johnson will start, even though Johnson has been with the Redskins for less than a week.
"He's always been a guy in the pocket who is pretty dangerous when he moves around, gets outside and he was familiar with the system and handled [it]," Gruden said Monday. "For the most part, he did a pretty good job with the snap count and formations and plays, so I think there is an upside there that we can build off of."
Johnson, who was signed last Tuesday, replaced Sanchez during Sunday's game and had more success than Sanchez in the loss.
Johnson's last start came on Dec. 4, 2011, and he is 0-5 as a starter in the NFL. In those five starts, he has thrown five touchdown passes and nine interceptions.
Despite not having thrown a pass since 2011, Johnson completed 11-of-16 passes for 195 yards, one touchdown and one interception while playing four possessions on Sunday. He also led the team with 45 rushing yards. All of Washington's points came on drives directed by Johnson.
"Yeah, you know when you watch Josh play, he can be hot and cold throwing the ball," Gruden said. "He can throw a great ball and then throw one in the dirt, then throw a great ball. The consistency probably is what people see. Now his age , he's a little bit older, guys want to go younger, try and go younger, try to get a younger guy in here. But, he's been on 11 or 12 teams. You can look at it as a negative or you look at it as a positive that he does have a skill set that's intriguing and when he gets an opportunity, like he did yesterday, he does pretty well. So, he'll get another big one on Sunday."
TE Jordan Reed suffered what was diagnosed with a toe muscle strain in Washington's loss to the Giants on Sunday. Reed was scheduled to have an MRI on Monday to provide more specific information on the severity of the injury.
Redskins head coach Jay Gruden did not sound optimistic on Monday when he said there is a "level of concern" with Reed's availability for the rest of the season.
"It's a pretty good strain," Gruden said. "We'll see if it's one week, two weeks or the rest of the year. We're not sure yet."
WR Josh Doctson was put in the concussion protocol on Monday. Gruden said he did not know when Doctson suffered the blow that led to his current status. "He checked in this morning with symptoms so we're checking him out," Gruden said. Doctson had four receptions for 84 yards on Sunday and has 39 catches for 469 yards and two touchdowns for the season.
LB Shaun Dion Hamilton suffered a shoulder strain and contusion on Sunday. His status for the next game is uncertain.
QB Mark Sanchez started Sunday's game against the Giants and went 6-of-14 for 38 yards, no touchdowns and two interceptions. He was also sacked five times before being replaced.