San Francisco 49ers quarterback Alex Smith will miss Sunday's game against the Denver Broncos in London, England, because of a separated left shoulder.
Head coach Mike Singletary said Wednesday that Smith will be sidelined for 2 to 3 weeks and Troy Smith will start for the Niners (1-6) at Wembley Stadium.
"Troy Smith gives us a good opportunity to win this game," Singletary said. "He has enough of the offence to play."
Alex Smith was injured on a sack in the third quarter of last Sunday's 23-20 loss to the Carolina Panthers. David Carr replaced him, but was passed over for this weekend's game.
"I talked to David Carr about it. He understands," Singletary said.
Troy Smith was signed in December and has not yet played a game for the 49ers.
The Niners have a bye following the game at Wembley, giving Alex Smith a chance to heal before San Francisco faces the St. Louis Rams on Nov. 14.
Alex Smith completed 9 of 19 passes for 129 yards and one touchdown against Carolina. But some confusion among his offensive linemen allowed Charles Johnson to tackle him from his blind side, driving his shoulder into the turf.
He arrived in London on Monday, along with the rest of the team, and spent the morning at the hospital, still with his non-throwing arm in a sling.
Both the 49ers and Broncos (2-5) are coming off losses and will be looking to get their season on track Sunday in the fourth regular-season NFL game to be played in the British capital.