Frank Gore told reporters he was suffering from a concussion Thursday, and the announcement turned into a small headache for the 49ers.

Coach Mike Singletary dismissed Gore's diagnosis by saying: "Frank Gore is a football player. He does not know what a concussion is. He has no idea."

Singletary said his star running back was suffering from a neck strain and would be fine to play Sunday against the St. Louis Rams.

Gore, upon further review, agreed. He ventured into the writers' room late in the day to say he had misspoken.

"My neck has been bothering me. I'll be all right. I just jammed it," Gore said.

The running back then expressed no doubts about being ready to face the Rams at Candlestick Park and said he would even return to practice today after a two-day absence.

Gore's status, of course, is at the center of the 49ers' universe. His 1,045 yards from scrimmage rank third in the NFL and represent 37 percent of the team's offense. DeShaun Foster, listed No. 2 on the depth chart, has 11 carries for 26 yards this season.

The injury saga began around 11:30 a.m., when Gore, looking downbeat, told a handful of reporters he suffered a concussion while blocking 6-foot-5, 247-pound defensive end Chike Okeafor during the final minute of a 29-24 loss to the Arizona Cardinals on Monday night.

Gore said he still had a "bad headache" from the Okeafor hit and recalled the concussion he suffered in 2006 against the Detroit Lions.

But shortly after practice ended at 3:45 p.m., Singletary tried to set the record straight.

The coach said he had "no idea" why Gore would describe his injury as a concussion when tests with trainer Jeff Ferguson had determined that it was a neck strain.

"He's going to play. I don't want to go into any other scenarios because he's going to play," Singletary said.

Gore came out of the Cardinals game for one play after Jason Hill made a catch at the 1-yard line. It was on that catch that Gore wound up crashing helmets with Okeafor.

Gore needed help off the field.

"He was tired, a little woozy, a little nauseous, but he's fine," Singletary said. "Trust me. Let me just say this, OK? I'm not a doctor, but I know when I hear 'concussion.'

"I talked to the trainer and (Gore) does not have a concussion. It's as simple as that. Guys get tired. I mean, we had guys getting IVs left and right, we had guys that were nauseous, we had guys throwing up, we had guys cramping up — all kinds of stuff.

"But I'm based on everything that I have from the trainer — and I get the report every day; he does not have a concussion. Anything else?"

About an hour after Singletary's press session, Gore ventured into the writers' room, accompanied by a member of the 49ers' public-relations staff.

Gore said his headache from earlier in the day had disappeared. He said part of the reason he was so downcast earlier was that he was consumed by frustration about his final run against the Cardinals.

On second-and-goal from the 1, Gore tried to go to the left side. But Okeafor reached through the line and got just enough of a hand on Gore for him to lose his footing.

Gore said his wooziness at the time might explain why he went down so easily.

"For me just to get rubbed like that, and I stumbled, that was tough on me," he said.

Gore lost yardage on the play, leaving the 49ers with one more shot. With Gore split wide left as a receiver, fullback Michael Robinson got the carry and was stopped from the 2½-yard line as time expired.

"We could have won a game," Gore said. "The type of player I am, I'm so hard on myself. I just wanted to make that play, and I didn't. I've just been thinking, and I've been frustrated and down.

"Coach (Mike) Martz told me, 'Don't worry about it.' He knows what type of player I am. Something just happened, you know?"