ST. LOUIS -- Rookie Zac Stacy has been a big part of the St Louis Rams' revitalized rushing attack.
But whether Stacy, who has rushed 141 times for 624 yards and four touchdowns, will get a chance to pound away at the San Francisco 49ers on Sunday is up in the air.
Stacy was one of three Rams players who left Sunday's 42-21 win over the Chicago Bears with concussion-like symptoms. Cornerback Trumaine Johnson and guard Chris Williams also were sidelined.
Rams coach Jeff Fisher said when a player has concussion-like symptoms, there is a process that must be followed before the player gets back on the field.
None of the three Rams who left against Chicago made it back into the game. It is not known yet whether they will be able to play against San Francisco.
"We have protocol," Fisher said. "We have evaluations (on the) sideline, inside and then the doctors make the determination. We have a series of things we do today, tomorrow and Wednesday; right now everybody's doing fine."
Fisher said that each player will take the baseline concussion test once, and then take it again before getting clearance.
"But everyone seemed to be feeling pretty well today," Fisher said.
Fisher is feeling pretty good about his running game.
Stacy ran 12 times for 87 yards and a TD against Chicago before leaving. He was replaced by Benny Cunningham, who had 13 carries for 109 yards and a score.
Overall, St. Louis ran the ball 29 times against the Bears for 258 yards.
Fisher said those numbers are a direct result of the team's efforts to stick with the running game.
"The last seven weeks, we're averaging 31 rush attempts per game and over 160 yards, about 4.9 per carry," Fisher said. "We focus on it and we stuck with it and we emphasized it and it's allowed us to be successful.
"We're pleased with it. But you have to stay consistent with it and do it week after week."
The Rams' average got a big boost against the Bears when wide receiver Tavon Austin ran it 65 yards for a touchdown on the third play from scrimmage.
The Rams' No. 1 pick took a pitch on a reverse while running left, then reversed field and took off to the right on a designed run.
The touchdown was Austin's first rushing touchdown and the Rams' longest rush since Hall of Famer Marshall Faulk had a 70-yard run on Dec. 23, 2001, that also went for a score.
Austin's run was the exception, with the norm being pounding away with Stacy and Cunningham. A rookie free agent from Middle Tennessee State, Cunningham had his first 100-yard game as a pro and his first touchdown.
"He's a great back," Fisher said after the game. "He really is. He's a great back and he works hard. I was excited to see him get an opportunity and make the most of it."
If Stacy cannot go on Sunday, Cunningham will again have to shoulder the workload in San Francisco.
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.