Alex Smith sprained his right knee in San Francisco's fifth straight loss, and the 49ers aren't certain their rookie franchise quarterback will play against Tampa Bay on Sunday. Smith, 8-of-16 for 92 yards and one interception in the Niners' humiliating 52-17 defeat, was hurt when his cleats got caught in the turf while LaVar Arrington tackled him in the first quarter. He played the rest of the game, feeling only momentary pain -- but after his knee stiffened up overnight, the No. 1 overall draft pick wore a heavy wrap and a brace Monday at the 49ers' training complex. He is listed as probable on the injury report, but the 49ers will wait until later in the week to determine whether Smith can make his third career start. Smith sprained two ligaments on the inside of his knee, and fluid built up behind his kneecap. Though he had previous back injuries from weightlifting, he had never been hurt while playing football in high school or at Utah. ``I guess that's why I do things like that,'' Smith said, referring to his dangerous attempt to make a play while Arrington was bearing down on him. ``Other people would have gone out of bounds or gone down. Obviously, I need to learn from that.''