PEORIA, Ariz. -- Among the questions facing the Mariners as they prepare to open Spring Training this week will be the health of outfielder Guillermo Heredia. And, in turn, should Heredia not be ready to start the season as he recovers from shoulder surgery, who steps up to fill the role of fourth outfielder on a team that is largely set in the position battles?
The acquisition of Dee Gordon to play center field this season set the stage for Heredia to be the backup at all three outfield spots, a role he handled well last year as a 26-year-old rookie. But Heredia played through a partial separation in his left (non-throwing) shoulder the final two months of the season and underwent surgery in October.
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If he's ready to go, the outfield is set with Mitch Haniger in right, Gordon in center and Ben Gamel in left, with Heredia able to platoon with Gamel in left or fill in at either of the two spots as needed.
But Heredia's availability is far from a certainty at this point, which could open the door for some interesting competition for the backup outfield spot to open the season.
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The only other outfielder on the 40-man roster at this point is Cameron Perkins, a 27-year-old who was claimed off waivers from the Phillies in December. He'd likely compete with Kirk Nieuwenhuis, one of several non-roster invitees who'll be in camp on a Minor League contract.
Nieuwenhuis brings the most experience to the table as a 30-year-old who has spent parts of six seasons in the big leagues with the Mets, Angels and Brewers while posting a .221/.311/.384 line with 31 homers and 117 RBIs in 414 games.

Perkins is a 6-foot-5, 205-pounder who is athletic enough to play all three outfield spots and put up a .288/.374/.447 line in 76 games at Triple-A Lehigh Valley. The Indiana native made his Major League debut for the Phillies last year and while he hit just .182 with one home run and eight RBIs in 88 at-bats, the Mariners are intrigued by his skill set.
"Cam Perkins is a good athlete," general manager Jerry Dipoto said. "He's got on-base skills. It was a depth move for us. He's been a good Triple-A player, he's got options remaining. He has some Major League experience. And from all we've been able to unearth, the makeup is great. So he's an athlete who's a hard worker and still a flexible roster piece for us."
The Mariners also figure to give a good look this spring to two of their young outfield prospects, Braden Bishop and Ian Miller.
Bishop, ranked as Seattle's No. 4 prospect by MLB Pipeline, runs extremely well and is a defensive standout in center.
"Braden had a heck of a year last season," Dipoto said. "He moved a couple levels and has always been one of our best defensive players in the system. He can really play the outfield, he's an athlete and his makeup is excellent."
Bishop, 24, hit .296/.385/.400 with 16 stolen bases in 88 games for Class A Advanced Modesto, then continued to flourish with a .336/.417/.448 line with six stolen bases in 31 games after being promoted to Double-A Arkansas.

"The big thing for Braden was taking that next step with his offensive approach and getting some consistency with the bat. This year even when he got to Double-A, it was a pretty good transition for him," Dipoto said. "He's a good-looking player, a good-looking athlete and just on his athletic and defensive ability, he's going to play in the big leagues. His bat will determine his role, but he has a lot of physical traits that are going to allow him to play, minimally as an extra guy."
Miller, the Mariners' No. 20 ranked prospect, also has outstanding speed and was the Mariners' Minor League Hitter of the Year last year while spending most of the season with Arkansas.
Miller, 25, stole a combined 43 bases between Arkansas and Triple-A Tacoma while batting .307, though that number dipped to .268 in 41 games at Tacoma.

Both Bishop and Miller will get their first taste of Major League camp when position players report next Monday. Mariners pitchers and catchers report for physicals Wednesday and will be on the field for the first time Thursday.