PEORIA, Ariz. -- Mariners left fielder Ben Gamel will almost certainly miss the start of the regular season as tests on his sore right side revealed a strained oblique muscle on Monday.
Gamel is expected to be sidelined for 4-6 weeks. Opening Day is March 29, when Seattle takes on the Indians at Safeco Field.
The 25-year-old Florida native felt something grab in his side while hitting in the cage on Friday and was scratched from the lineup that afternoon. The injury was expected to sideline him for only a few days before team doctor Ed Khalfayan reviewed MRI test results on Sunday.
Gamel was one of the Mariners' pleasant surprises last season, hitting .275/.322/.413 with 11 home runs, 59 RBIs and 68 runs in 134 games as a rookie.
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The Mariners have been shorthanded in the outfield already this spring with right fielder Mitch Haniger yet to play in any Cactus League games as he rests a sore right hand. Haniger was cleared to begin swinging a bat on Friday and could be worked into games later this week.
Guillermo Heredia was expected to open the season as the fourth outfielder, but figures to move into Gamel's spot in left field for now. Heredia, however, is just returning himself from October surgery on his right shoulder.
Heredia has played in the past two Cactus League games, going 1-for-2 with a double and three walks as a designated hitter, but won't be allowed to play in the field for another week to 10 days.
Converted second baseman Dee Gordon has looked good in center field, but the Mariners are now thin in the corners. Cameron Perkins and Junior Lake, two 27-year-olds with some Major League experience, are among the options.
Lake was signed to a Minor League deal at the start of camp. He has a .235/.278/.376 line with 17 homers in 223 games with the Cubs, Orioles and Blue Jays, but hasn't been in the Majors since 2016. Perkins was claimed off waivers from the Phillies in the offseason after batting .182 in 88 at-bats as a rookie.
Kirk Nieuwenhuis, a 30-year-old with a career .221/.311/.384 line in 414 games over six seasons with the Mets, Angels and Brewers, is also in camp on a Minor League deal, but he's currently sidelined by a strained hamstring.
Two young prospects, Braden Bishop and Ian Miller, are both strong defenders who have played well this spring and figure to get longer looks. Bishop, the club's No. 5 prospect as ranked by MLB Pipeline, has never been above Double-A, but the 24-year-old is 7-for-15 with a double and triple in early Cactus League play.
Miller is a 26-year-old speedster who was Minor League Hitter of the Year last season while splitting time between Double-A Arkansas and Triple-A Tacoma. He's 4-for-15 with five RBIs and a stolen base this spring.
There are also some veteran outfielders on the free-agent market if the Mariners decide to add options, including long-time Seattle star Ichiro Suzuki, who is still hoping to continue his career at age 44 after hitting .255/.318/.332 with three homers and one stolen base in 196 at-bats last year for Miami.
Carlos Gonzalez, a younger option at 32, is also unsigned. The three-time All-Star and Gold Glove winner hit .262/.339/.423 with 14 homers in 470 at-bats for the Rockies last season.
Jonathan Jay, a veteran the Mariners pursued early in the offseason before trading with the Marlins for Gordon, is also still available, as are Jose Bautista, Melky Cabrera and Seth Smith, another former Mariner.