ST. LOUIS (AP) -- Running back Zac Stacy, one of three Rams players who left Sunday's 42-21 win over the Chicago Bears with concussion-like symptoms, has been cleared to play at San Francisco on Sunday.
Cornerback Trumaine Johnson and left guard Chris Williams also were sidelined with blows to the head, but will be available against the 49ers.
All three returned to practice in a limited role Thursday, then were full participants Friday at Rams Park.
None of the three Rams who left against Chicago made it back into the game. Williams left in the second quarter. Stacy and Johnson both were hurt in the third period.
All three have been cleared to play against San Francisco (7-4).
Stacy briefly saw action for St. Louis in its first game against San Francisco before he became the starter. To see playing time this week, he had to be medically cleared.
''I'm good to go,'' said Stacy, who rushed for 87 yards and a touchdown before leaving the Bears game. ''I took the tests and they came out well. They take these precautions.''
Stacy has been a big part in the resurgence of the Rams. He has scored five touchdowns in the last five games and rushed for 100 yards in back-to-back games against Carolina and Seattle. He is second among all rookies with 624 yards.
''I was disappointed to have to come out because I want to help my team,'' Stacy said. ''I felt like I was fine. Absolutely, it was hard to come out of there, but you have to do what the doctors say.''
The Rams (5-6) will be trying to get back to the .500 mark for the first time since Oct. 13, when they were 3-3 after beating Houston 38-13.
Rams coach Jeff Fisher said that each player took the baseline concussion test earlier in the week. They all underwent a final neuro-psychological testing. Once that test was passed, they were given clearance.
''We have protocol,'' Fisher said. ''We have evaluations (on the) sideline, inside, and then the doctors make the determination. All three of them are doing well.''
The players said they agree with the protocols put in place by the NFL.
''They had to do their testing and all that kind of stuff,'' said Williams, who is in his sixth season and is a former Bear. ''At the time, it's frustrating because you want to play and we were playing Chicago. You know, the protocols are implemented to protect us, so you really can't argue with that.
''Obviously, there are long-term effects with brain damage and that kind of thing. You don't want that to happen.''
The concussion was Johnson's first, he said, since he was in high school in Stockton, Calif., when he was a receiver. The second-year pro got into a collision Sunday and was down on the field before walking off with assistance.
''I remember waking up and seeing (head athletic trainer) Reggie Scott's face and that was about it,'' said Johnson, who has five starts and two interceptions this season. ''It was big-time scary when you can't remember things like that. I just pray to God that I'm not hurt now and that I've been cleared to play. I'm happy I'm back.''
The game against San Francisco is one Johnson did not want to miss. He grew up a fan of the 49ers and Jerry Rice. Johnson will have many family members and friends at the game, which will be the last for the Rams at Candlestick Park.
''This is a big week; I'm going home,'' Johnson said. ''I wanted to get back on the field as quickly as possible but, at the same time, you want to be safe.''
NOTES: RG Harvey Dahl was limited in practice Friday. He is listed as questionable. Dahl has missed the last three games because of a knee injury. ... S T.J. McDonald (shin) was limited in practice and is listed as questionable. ... CB Brandon McGee (foot) did not practice but is listed as questionable.
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