Boston Red Sox manager John Farrell has some pressing decisions to make as he observes his players during spring training. Perhaps the first line of order is choosing a starting center fielder, which will either be Mookie Betts or Rusney Castillo.

At this point in the competition it looks as if Betts has the edge, and it could stay that way. The 22-year-old was batting leadoff with the rest of the Red Sox starters on Tuesday while Castillo was penciled in as a starter with the backups and minor leaguers in the second game of the team's doubleheader. On top of that, Castillo suffered an injury in that game.

"Castillo lined the first pitch he saw Tuesday into center for a single in the [Boston College] game," writes Sean McAdam of CSNNE.com. "He later felt some soreness in his left side after his final at-bat and will be re-evaluated Wednesday morning."

"He felt some soreness in his left side, so we've got to reexamine him," added Farrell, via Ian Browne of MLB.com. "I don't know specifically yet, but there's a little soreness there in the left side."

Castillo will be visiting the medical staff on Wednesday to get checked out for the potential injury. If it happens to be an oblique, the Cuban defector will surely miss some time in spring training, which will significantly affect his chances of being the starting center fielder for the Red Sox on Opening Day. Farrell said the team is getting more familiar with Castillo as they see him in action more often, but that could now become an issue.

Although Betts was leading off with the starters on Tuesday, Farrell said he "wouldn't read anything into it" because the two outfielders are going to get equal reps and it just so happened that was Betts' first assignment. After all, the prospect played 52 games with the Red Sox last season compared to Castillo's 10.

Once Castillo pays his visit to the medical staff there will be more information regarding his status for the near future. If he happens to be sidelined for some time, it wouldn't be surprising if Betts ran away with the starting job if he continues to perform.

UPDATE: Castillo was diagnosed with an oblique strain and will miss at least a week.