Yoenis Cespedes, Jay Bruce, Juan Lagares, and Brandon Nimmo will be the four full-time outfielders on the Opening Day roster. With Michael Conforto being injured, the Mets are in need for some outfield depth.
Reyes played some outfield in 2017 and the reviews were generally positive. He played 5.1 innings in left field where he posted a 0.6 UZR and -1 DRS. He also played one inning in center field but did not have anything hit to him. He has the tools to be a decent outfielder, being that he has speed and a strong arm.
Wilmer Flores, on the other hand, has no exposure to the outfield. He is not a fast runner but does have a strong arm to somewhat make up for his lack of speed. As he doesn’t have a position in the infield, it couldn’t hurt to try him in the outfield in an effort to make sure his bat is in the lineup as often as possible, especially against lefties.