Alex Smith has said that "it sucks" to be replaced in the San Francisco 49ers' starting lineup.

The NFL pass completion percentage leader has recovered from a concussion that forced him to miss a game, but coach Jim Harbaugh has been impressed by backup quarterback Colin Kaepernick.

Smith told Comcast SportsNet: "I mean, it sucks. I don't know what else to say."

He also spoke to the Associated Press, adding: "It stings the most just because I really felt there was something special going on here, and you sacrifice and invest so much time.

"I have no idea what's going to happen from here. All I can do now is just prepare and get ready."

The 49ers face the St Louis Rams this Sunday.