Shanahan saw enough of Grossman after four interceptions, pulling him in favor of John Beck to start the fourth quarter. The Redskins trailed 20-6 at the time.
Fresh off that performance, Shanahan declined to name a starter for next week's game against the Carolina Panthers. He said that announcement will likely come Wednesday.
"I would never announce that after the game," he said. "We would make announcement until after we watch the film."
Beck completed 8 of 15 passes for 117 yards and no interceptions in what was his first regular-season game since Dec. 30, 2007, during his rookie season with the Miami Dolphins.
"Number one, we needed a spark," Shanahan said after the game. "John practiced very well. ... With four turnovers there, we thought it was time to make a change."
Grossman's four turnovers Sunday brought his season total to 11.
A solemn Grossman addressed reporters after the game.
"There were a lot of things that were a problem today," he said. "I didn't execute. I'm sure most of the questions are going to be about the interceptions so I might as well go over them with you."
Grossman then when through his picks -- he needed a reminder for the second pick -- chalking the turnovers up to a combination of bad throws and receivers' inability to cross defenders.
"Ultimately I'm responsible for the football," Grossman said. "There's so many times in this league that you face adversity for some reason or another. ... I believe in myself no matter if the whole stadium doesn't, the coaching staff doesn't. I believe that every single play I'm going to get it done."