FORT MYERS, Fla. -- Burke Badenhop has been working on a different slider this spring in the hopes of having more success against left-handed hitters.

"My slider typically is more 'slurvey,'" Badenhop said. "I was trying to throw a cutter, and it turned out to be a true slider. It's a little firmer, it's a little shorter, it's on the plate longer. It's been pretty decent so far. I'm pretty happy with that."

Badenhop, 28, was acquired from the Marlins in exchange for Minor League catcher Jake Jefferies on Dec. 12. Badenhop went 2-3 with a 4.10 ERA in 50 games for the Marlins in 2011. The Marlins used Badenhop as an all-around reliever. The Rays see him as a pitcher who can use his sinker to get a ground ball when needed. Badenhop allowed just one home run last season, and his 74.2 percent ground-ball percentage ranked sixth highest among National League relievers.

Given those numbers, Badenhop's sinker remains his money pitch.

"I like his breaking ball," Rays manager Joe Maddon said. "It doesn't give up, it keeps breaking. It has a lot of spin on it. He's able to throw it to both sides of the plate, which I like. I like his sinker."

The Rays will have 12 pitchers on their staff this season, seven of which will be relievers. Looking at the bullpen, Kyle Farnsworth, Joel Peralta, J.P. Howell, Fernando Rodney and Jake McGee appear to be locks, with the odd man out of the starting rotation to also be added (Maddon said that decision will likely be made Tuesday). That would leave Baddenhop and Brandon Gomes contending for the final bullpen spot.

Gomes, who had minor back surgery in the offseason, has not had his best velocity this spring. But the right-hander made a good accounting for himself last season.

"This guy was a big part of the end of last season, man," Maddon said. "I can't say it enough, how much I, and we, appreciate his makeup."

Jennings among injured Rays working back

FORT MYERS, Fla. -- Updates on the walking wounded continue to be the story of the day for the Rays this spring.

"They're all making some progress," manager Joe Maddon said.

Maddon called Reid Brignac (right foot soreness) "day to day." The skipper also noted that B.J. Upton (lower back) wanted to "get much more active today." Sam Fuld (right wrist) said he would be having an MRI on Monday. Meanwhile, Desmond Jennings (right shoulder) appears close to returning to playing in the field, though Maddon wants to proceed with caution.

Jennings was scheduled to play catch in Port Charlotte on Monday, then play designated hitter in a Minor League game.

"I don't want to press his arm or push his arm," said Maddon, when asked if Jennings would play in the field Tuesday against the Red Sox. "Maybe DH, maybe the outfield. I'm not sure. I have to get the report back from [head athletic trainer] Ron [Porterfield]. This is something Ron likes what he's doing, likes the progress.

"But he's also seen this kind of a soreness in the past, where if you don't take care of it, it can be more lingering. So great progress -- he didn't feel anything in a bad way yesterday. So it's getting better. When is the time to push him? I don't know if it's tomorrow, yet."

Maddon said Jennings or Upton could be the DH against the Red Sox or play in a Minor League game in Port Charlotte.

Jennings said he could easily play if it was the regular season.

Rays unveil three more summer concerts

FORT MYERS, Fla. -- The Rays announced Monday that LL Cool J, Earth Wind & Fire and the "World's Biggest Preschool Band," The Wiggles, will be among the acts performing at Tropicana Field this summer as part of the 2012 Summer Concert Series.

LL Cool J returns to The Trop for the second time, as he is scheduled to perform at the conclusion of the Rays-Orioles game on June 2. Earth Wind & Fire will perform following the Rays-Tigers game on June 30. The Wiggles make their second appearance at Tropicana Field on Aug. 5, when they perform after the Rays-Orioles game as part of Family Fun Day presented by the Tampa Bay Times.

The Rays previously announced that ZZ Top, 3 Doors Down and Gretchen Wilson will all perform at Tropicana Field following the Rays-Marlins game on June 17.

The concerts are free with the purchase of that date's game ticket. The remaining concert dates will be announced soon.