Seth Lugo brought his platinum blond locks to Citi Field for a workout Friday afternoon, but unfortunately for the Mets, that’s not his only holdover from the World Baseball Classic.

Lugo’s spot on the roster may be in jeopardy as he battles arm fatigue, manager Terry Collins said. The Mets will make a decision on whether Lugo, who pitched for Puerto Rico in the WBC, or Rafael Montero will earn the long-man role come Opening Day on Monday. Lugo pitched 15 innings in the WBC, 6 1⁄3 innings more than Puerto Rico’s next innings leader.

“Of all the pitchers we had in spring training, he was probably the one that was tested the most because of the WBC, and I think he was a little fatigued at the end, and I want to make sure he’s OK,” Collins said. “The other day, his arm felt — of all the guys, we didn’t hear the word dead arm at all, all spring — he was the one guy that said, ‘Hey, look, I’m having a little arm fatigue right now.’ ”

Lugo said he started to experience the fatigue after his final exhibition start and believes it will clear up soon. A big part of it, he said, is that he knew he was competing for a spot and might have unduly stressed his pitching arm.

“It’s very tough,” Lugo said of finding the balance between competing and resting. “Personally, I think that might’ve been where I got my arm a little tired, just trying to do too much in that last outing in spring, to have the same intensity I had in the World Baseball Classic. I think I just didn’t know that I needed to back off a little bit and focus on getting ready for the season.”

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The way Collins framed it, the spot appears to be Lugo’s to lose, but if he feels ill effects from his Friday session on Saturday, there’s every chance Montero could swoop in and grab it.

Lugo came up last year, going 5-2 with a 2.67 ERA, and helped save a Mets team that was thin on pitching because of injuries to three-fifths of its rotation.

“I think just take a day or two and I think it would be better than try to push through a little arm fatigue,” Lugo said. “If I can be on the team, that’s where I want to be. If I can be in the bullpen, so be it. The way the year ended last year, I think I had a little more confidence coming out of the bullpen. Last year, just coming up, I was fresh in the big leagues, so I think it could be interesting out there.”

Walker stock on the rise

After an injury-shortened season that might have hampered his free-agency prospects, Neil Walker is back and healthy for the Mets, and Collins believes this could be a big year for his second baseman. “When you get good players and they’re challenged because their occupation is on the line, they pick it up,” Collins said about Walker, who’s again up for free agency at the end of the season. “I think Neil is going to have a good season. He’s a leader in his own sort, in his own way. He’s not afraid to say something. He’s brought some credibility to his team because of his time and what he’s done . . . I’m anxious to keep him out there all summer.”

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Walker hit .282 with 23 home runs and 55 RBIs in 113 games last year before undergoing season-ending back surgery.