The Rays, meanwhile, will be holding their breath as right-hander Alex Cobb takes the mound against Haren in his first start after a wicked line drive hit by Ichiro Suzuki off his leg force him out of the game after pitching just two innings against the Mariners.
Haren originally was scheduled to pitch Saturday, but he was moved up when the Angels decided to skip the struggling Santana and give him a few days to work on the problems that have made this a tough and disappointing season for him.
Because of Thursday's off-day, Haren will be pitching on normal rest as will lefty C.J. Wilson on Saturday.
Haren is coming off a determined performance last Sunday, when he pitched six innings, giving up three hits and two runs in a 7-4 victory that gave the Angels a series win over the American League West-leading Rangers.
Haren is 7-8 with a 4.76 ERA in 18 starts and has bounced back nicely after being bothered by back problems earlier in the season.
"I feel great right now," Haren said on Wednesday. "I don't really like to put percentages on things, because I don't really know how to gauge my body that well. It's just a matter of taking care of it. It's not something that's going to affect my career."
Does he expect the back pain to linger through the season?
"A nagging injury will, a lot of times, feel better in the next couple days," Haren said. "As a starting pitcher, you go through playing 100-plus [pitches] out there and you aggravate it again. Hopefully, I've conditioned my body to withstand throwing all those pitches."
Cobb, 4-7 with a 5.08 ERA in 11 starts, made a nifty play after taking Ichiro's second-inning shot off his leg.
The right-hander chased down the ball after it went toward the plate and flipped it to catcher Jose Labaton, who tagged out Carlos Pequero as he tried to score from third.
Cobb went down to the ground after the inning-ending play and needed assistance to leave the field. He allowed two runs, three hits and two walks in two innings.
"Once they saw me on the ground, I figured I probably wasn't going to be able to get back out," Cobb said. "But I'm probably very fortunate that it wasn't fractured."
The ball hit him in a good place, Cobb said.
"Right in between the fibula and the tibia," Cobb said. "Fortunately it got all muscle, no bone, so there's no fracture. I should be fine."
Rays: Bullpen rolling along
The Rays' bullpen had its 21-inning scoreless streak come to an end in Thursday's 6-2 loss to the Orioles, but the unit's recent string of success has still been a welcomed treat for manager Joe Maddon.
Though Maddon isn't necessarily surprised by his relievers' domination of late, he admitted managing the bullpen is always one of the most stressful aspects of his job.
"You're not going to go to the final game of the season and win it without strong starting pitching and a great bullpen," Maddon said. "We have a nice balance back and forth, they seem to be relatively well and healthy. I think going into the last two months of the season for me, as a manager, I know that it's important to keep these guys frisky and fresh. If there's anything I agonize over on a daily basis, it's the bullpen. I don't agonize over anything else. I promise you that."
Angels: Aybar nursing big toe injury
Shortstop Erick Aybar hasn't played since Saturday after fouling a ball off his right big toe, and if he is not making significant progress by the weekend towards being able to play, manager Mike Scioscia said a decision regarding a trip to the disabled list will have to be made.
Either way, the injury isn't something the Angels feel will keep Aybar out long term.
First baseman Albert Pujols did not play in Wednesday's 11-6 victory over the Royals and Scioscia was hopeful the first baseman would return to the lineup on Friday after Thursday's off-day. X-Rays taken on Pujols' arm on Wednesday were negative.
The Angels are 35-13 in their last 48 home games against the Rays, but were swept in their first 2012 series at St. Petersburg April 24-26.
Ben Zobrist is just 2-for-21 with six strikeouts in his career against Haren. The .095 average is his lowest against any pitcher whom he's faced 20 or more times.