What if the Boston Red Sox’s opening day second baseman isn’t Kristian Campbell, Alex Bregman or David Hamilton?

The battle seemingly was down to those three after Vaughn Grissom was optioned to minor league camp earlier this week. And multiple recent reports indicated Campbell, a consensus top 10 prospect in baseball, was the favorite to win the job.

However, there’s momentum behind top prospect Marcelo Mayer, who’s outperformed Campbell and Roman Anthony this spring and saw increased work at second base this week. Mayer’s future probably is on the left side of the infield, but one MLB scout told The Boston Globe’s Alex Speier that the Red Sox should open the season with Mayer at second base.

“I’m not surprised he’s getting time (at second),” the scout told Speier for a piece published Thursday. “I think we’re seeing what this guy’s capable of. … Marcelo can play defense better than all of them except maybe Hamilton. He can certainly hit well enough to play there every day. … This would be the high-risk, high-reward option. The downside is he has zero big-league experience.

“He has the most upside in the organization outside of (Roman) Anthony. Simple as that. Do you want to start the [service time] clock and have him play every day? … If it were me, I’d roll with Marcelo. I’d go with Marcelo and Hamilton and say, ‘This is our best team.’ ”

Entering Thursday, Mayer had a .355 batting average and 1.025 OPS with one homer, nine strikeouts and five walks in 31 spring training at-bats. Hamilton and Campbell had averages of .239 and .158, respectively.

As for Bregman, all signs point toward him opening the season at third base — much to the dismay of Rafael Devers. Boston’s star slugger reportedly considered requesting a trade midway through the spring amid his dismay over Boston’s preference for Bregman playing third.

The Red Sox will kick off their season next Thursday when they visit the Texas Rangers.