Stacy's status was in question after the second-year player left the Rams' game last week at Philadelphia because of a calf strain. After missing practice early in the week, he was back in full swing Friday and Saturday.
''I had a good week of prep this week, got back running around earlier this week,'' Stacy said. ''It feels good, ready to go.''
Rams coach Jeff Fisher said Stacy responded well as a full participant in practices Friday and Saturday.
''Usually, if there's any doubt in our minds, we'll list him as limited and questionable, but he will be listed as full practice, probable,'' Fisher said.
After running for 973 yards last season, Stacy has struggled to gain traction through the first four games. Stacy has rushed for 223 yards on 53 carries and has scored only one touchdown.
The Rams are 19th in rushing - and it won't get any easier against a San Francisco defense ranked fifth against the run.
''Just watching them on film they run to the ball pretty good,'' Stacy said. ''It's just one of those games you'll get two yards here, you may lose a couple here and then you might pop one for 10. It's all about a grind, keeping the running game moving. It comes down to execution.''
Benny Cunningham provided a spark to the St. Louis running game after taking over for Stacy against the Eagles. Cunningham rushed for 47 yards, averaging 6.2 yards a carry, and scored a touchdown in the Ram's 34-28 loss.
Even with Stacy healthy, Cunningham should still see some touches against the 49ers. He hopes they can build off the momentum at the end of the Philadelphia game.
''Austin Davis had an excellent game, the offensive line started to open it up in the end,'' Cunningham said. ''If they come out and play the way they did, there's no doubt that we'll have success in the backfield.''
A strong running game could be essential to take the heat off of Davis, who will be making his second start since being officially named the starting quarterback over Shaun Hill.
Rams offensive lineman Rodger Saffold said San Francisco presents a challenge.
''We're going to have to focus on making sure we're efficient in our schemes and making sure we're going to right guys,'' Saffold said. ''After that, we're going to have to make sure on our one-on-ones that we set firm and don't give up a lot of penetration so (Davis) can see where to throw the ball.
''As far as the running game goes, basically it just means being efficient, having a good balance between rushing attempts and completions with our wide receivers. If we have a good balanced game, I think we can put ourselves in a good position to win.''
NOTES: Stacy (calf) was a full participant and is probable, as was Eugene Sims (groin) and Kenny Britt (knee). Barrett Jones (back) and Jo-Lonn Dunbar (groin) were limited and are questionable. Alex Carrington (knee) and Chase Reynolds (hip) did not practice and are questionable. Trumaine Johnson (knee) and Brandon McGee (foot) did not practice and are out.