Pena -- who has been sidelined with plantar fasciitis in his right foot since Saturday's contest against the Yankees, when he exited in the sixth inning after hitting a fly ball to right field -- was placed on the DL prior to Friday's affair against the Blue Jays.
The move was retroactive to Sunday. Right-handed pitcher Dale Thayer was recalled from Triple-A Durham to fill the vacant roster spot.
In 45 2/3 innings with Durham this season, Thayer posted a 2-1 record with a 3.35 ERA. The 29-year-old's previous appearance with the Rays came on Oct. 4, 2009, when he pitched two scoreless frames vs. the Yankees.
With Pena ineligible to come off the DL until August 16 when the Rays welcome the Rangers for a three-game series at Tropicana Field, Ben Zobrist and Dan Johnson will pick up the slack at first base. Skipper Joe Maddon said he intends to get Johnson in the lineup as much as possible against right-handers. Zobrist got the start at first Friday night against southpaw Brett Cecil.
Pena felt he could have played with the injury, but he understood the team's decision.
"Last night, and [Friday] in the morning, they brought it up. I wasn't too happy, to be honest, because I want to be out there playing," Pena said. "I felt confident I would be able to [recover] within a short amount of time, within a couple of days. I thought maybe tomorrow I would be able to play. But after talking to the doctors and to [manager Joe Maddon and the medical staff], we looked at it in a different way.
"Would I rather play eight weeks at 75 percent or seven weeks at 100 percent? For me, it's a no-brainer -- I'd rather play seven at 100."
Like Pena, Maddon believed the move to be more precautionary than anything. He added that plantar fasciitis is difficult to diagnose, and often the best method of recovery is simply rest. Maddon was also inclined to add another reliever to a taxed bullpen.
"The bullpen right now, we just need to augment that group," Maddon said. "These guys have been doing an absolutely phenomenal job, and if we keep asking them to do too much, their effectiveness is going to go away. So we wanted to make sure we were totally stockpiling in on the bullpen."
Despite his disappointment, Pena will continue to partake in baseball activities over the upcoming week and fully expects to return to the lineup when eligible.
"I wasn't too thrilled when I heard it," Pena said. "I tried to do everything I could to not allow it to happen. But when you objectively look at it, they're trying to protect me, the team and our season."
James Hall is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.