Franklin Gutierrez will have an MRI exam Thursday to determine the extent of his latest injury, a hamstring strain that landed him on the 15-day disabled list Tuesday.

The Mariners called up Carlos Peguero from Class AAA to add an extra outfielder for the time being. Mariners manager Eric Wedge said he doesn't know how long Gutierrez will be out this time as he tends to the hamstring as well as pelvic and hip issues.

"I hope it helps him because the other issue is his hips," Wedge said. "So, hopefully he can use that time to help with that, too."

Peguero was chosen despite the fact Eric Thames has put up better hitting numbers down in Class AAA. The Mariners say they like Peguero's outfield defense and baserunning ability better at this stage and are eager for a look at Peguero's more patient plate approach against big-league pitching.

The burly slugger had upped his walk rate from 9 percent last year to 14.9 percent this season with Tacoma as he tries to be more selective with the pitches. His strikeout rate is also down, from 32 percent to 24.3 percent.

Peguero always has shown power in the minors, but has trouble connecting against better big-league hurlers. He made a concerted effort at spring training to bolster his plate discipline.

"I understood myself and what I had to do, what I'm capable of," he said. "And what I had to do to make an adjustment. To recognize me, myself, and not try to do too much."