Already playing without a full deck, LSU at least momentarily lost its ace in the hole in senior closer Hunter Newman, who will need at least two weeks — and possibly much more — to recover from a back injury.

LSU coach Paul Mainieri did not have specifics on what type of injury Newman suffered or a clear time frame for how long Newman would have to miss. In the meantime, he said sophomore right-hander Caleb Gilbert would be bumped into the closer’s role.

“He’s going to be out for a while,” Mainieri said. “We don’t know how long — it could be two weeks, it could be six weeks, we’re just not really sure yet.”

Mainieri said Newman will be re-evaluated in a week.

This is the latest significant blow to a team that has already lost anticipated cleanup hitter Bryce Jordan and setup man Doug Norman for the season. LSU also narrowly dodged an injury to Greg Deichmann, who fractured three bones in his cheek when he was struck in the face by a pitch in practice a week before the season.

Mainieri said Newman first noticed discomfort in his lower back last Friday, but he didn’t let the coach know about it. Newman then pitched a scoreless inning with two strikeouts in Sunday’s win against Wichita State.

“Then on Monday, I was told he was having some symptoms that indicated there was possibly some kind of issue with his lower back,” Mainieri said. “We sent him to get an MRI on Tuesday, and right before the game on Tuesday … I got the bad news.”

Mainieri said the MRI showed “an irregularity in his lower back, and consequently there’s one course of action that’s being tried right now.”

That course of action would hopefully put Newman on track to return at the shorter end of his recovery timeframe. If it doesn’t work, Mainieri said, “there might be something more drastic that needs to be done.”

With Newman and Norman out of commission, LSU is suddenly thin when it comes to back-of-the-bullpen arms.

“Those are two big blows to our team,” Mainieri said. “We can’t deny that.”

Gilbert transitioned into the setup man role after Norman’s injury and has performed well. In 14.1 innings this season, Gilbert has allowed just two earned runs — only one out of the bullpen, on a solo home run against McNeese — and has struck out 18.

The hard-throwing right-hander also has closing experience from his freshman season. He said he’s approaching this with a “backup quarterback mentality.”

“It’s Newman’s job, and when his time comes, he’ll get it back,” Gilbert said. “I’m just trying to fill the void and get those last three outs. I know what it takes, just from last year. I had some successes with it, I had some failures ... but at least I have some experience with it.”

But Gilbert can’t throw in every game, and beyond him, the Tigers are short on options with experience in late-inning relief.

Freshman right-hander Zack Hess could be a candidate to fill in Gilbert’s setup role, though he won’t be available to pitch until Sunday after throwing 75 pitches in a start Tuesday.

Fellow freshmen Todd Peterson and Matthew Beck could be asked to shoulder larger roles, as could junior Austin Bain and senior Russell Reynolds, both of whom have worked mainly in long relief this year.

“Somebody’s going to have to be able to bridge the gap between our starters and Caleb,” Mainieri said. “There’s guys there that we’re just going to have to change their roles. They’re going to be counted on more to get the job done in the latter innings for us.”

The way Mainieri looks at it, he and his team can take one of two routes.

“You can sit around and pout and wine about it and make excuses,” Mainieri said. “Or you can roll up your sleeves and challenge guys to take advantage of the opportunity and get the job done for us.”

Follow Luke Johnson on Twitter, @ByLukeJohnson.