ASHBURN, Va. — Donovan McNabb has been learning the Washington Redskins offense almost from the day he was traded in April, through spring practices, minicamps, training camp, midweek regular season practices and countless meetings with the coaching staff and the team's other quarterbacks.

Yet, with the game on the line against the Detroit Lions, Mike Shanahan decided McNabb wasn't competent enough to stay on the field. The coach made a stunner of a move, yanking his offensive captain from the game and inserting Rex Grossman, a decision that has ramifications for the rest of the season and into 2011.

"For him to be pulled like that, it's definitely a shocker to a lot of us," cornerback DeAngelo Hall said Monday. "It does raise the interesting point: After the season, will he be here or not?"

The switch to Grossman, which came with the Redskins trailing by six with 1:50 to play, didn't work. The backup's first snap of the season turned into a touchdown for the other team, with Grossman fumbling the ball on a blindside sack and Ndamukong Suh returning it for the score. Detroit won 37-25, leaving the Redskins (4-4) at .500 and still competitive in the NFC East as they enter their bye week — a sentiment that instantly took a back seat at Redskins Park in the wake of Shanahan's vote of no-confidence in his six-time Pro Bowl quarterback.

"We were kind of questioning what was going on," said guard Kory Lichtensteiger, expressing the mood in the huddle when Grossman entered the game. "But that's not our job, to figure out what the coaches were thinking."

Shanahan justified the move by citing the complexities of the two-minute offense. The game speeds up. Multiple plays have to be called at the line of scrimmage. It all has "to come automatically," the coach said after the game. Grossman spent last year in this same offense under offensive coordinator Kyle Shanahan — both were with the Houston Texans — although Grossman was a rarely used backup who didn't run the two-minute offense in a regular season game.

Yet, if McNabb hasn't grasped the offense enough to run a two-minute drill after seven months of study, there seem to be only three possible conclusions: The offense is too complex, the coaches have done a poor job teaching it, or McNabb is a poor student.

Or it could be a combination of the three.

Grossman said the Redskins' two-minute offense isn't more complicated than any he's run with other teams, but he did indicate he didn't have a full grasp of it until returning to run it for a second season.

"Last year I knew I could do it," Grossman said. "But until you have a couple of months to digest, get away from football and come back and really get a chance to study and do it again for the second time, that definitely helps."

Then there's McNabb's history. One of the knocks on McNabb in his 11 years with the Philadelphia Eagles was his struggles in the two-minute offense — which came to light most embarrassingly when he took his time leading a drive late in the Super Bowl with his team trailing and the clock ticking away.

For the record, the only time he was actually benched in Philadelphia came on Nov. 23, 2008, when he threw two interceptions and lost a fumble before getting pulled at halftime of a 36-7 loss at Baltimore. He started the following game and led the Eagles to a 4-1 record down the stretch and back into the playoffs.

McNabb did not speak to reporters Monday, but on Sunday he handled his benching without making so much as a ripple. He said he would have liked to finish the game, but the coach makes the decision. His slow pace in mastering the new offense has been one of the developing stories since the start of training camp, and he said he expected to be farther along.

"I thought we would get things rolling by now," McNabb said. "When you spend 11 years doing anything, then you go to something new, there's a big change. But that's the past. My comfort level in this offense is good, and we just have to make sure we can be consistent in execution."

McNabb is on pace for his worst season since his rookie year, when he only started six games. He has a 76.0 rating with only seven touchdown passes, and his eight interceptions have caused him to lose his prized spot as the NFL's all-time leader in interception percentage.

Shanahan said after the game that McNabb will remain the starter. The coach was expected to address the issue again at his weekly news conference Monday afternoon.

The Redskins gave up two draft picks for McNabb, who turns 34 this month and whose contract expires at the end of the year. Those draft picks would appear to be a waste if McNabb isn't signed to a new deal, but contract talks have been virtually nonexistent — Shanahan said he doesn't concern himself with such things during the season, anyway — raising more questions about a veteran who has quickly become a popular player in the locker room.

"As far as lingering effects of him getting benched, we don't know what to expect yet," Hall said. "We haven't had that happen before."