BOSTON — The storyline at Fenway Park this weekend revolves around Rafael Devers, but the Giants had quietly anticipated a different homecoming. Marcelo Mayer, the 23-year-old infielder acquired in a deadline deal with the Red Sox, was expected to make his Giants debut against the team that drafted him fourth overall in 2021. That plan has been derailed by a setback. Mayer’s rehab assignment with Triple-A Sacramento has been halted after he experienced soreness in his right foot. The injury traces back to a bruise sustained during his time with Boston, and the Giants are taking no chances. An MRI and CT scan confirmed the bruise, and the decision was made to have Mayer rest entirely over the weekend back in San Francisco. “He just aggravated it a little bit from being back out there every day,” manager Tony Vitello said during his pregame media session at Fenway. “He’s just going to take the weekend off and then kind of reassess things later.” The Giants had been carefully managing Mayer’s return. He missed time earlier this season with a stress reaction in his forearm, but that issue had resolved. In four rehab games, he showed promise, going 6-for-17 with solid contact. The original hope was to have him ready by the end of the Giants’ series in Cleveland, which would have allowed him to start at Fenway Park on Friday. Instead, the foot soreness has forced a delay. The Red Sox traded Mayer in a surprising move earlier this month, sending him to San Francisco in exchange for lefty Erik Miller, who has pitched effectively for Boston. The trade shocked many, as Mayer was considered a top prospect. Now, the Giants are eager to see what he can bring to their infield, particularly at second base. Vitello indicated that Mayer might not need additional minor league games if he is cleared to return soon. “I think he wanted to play here,” Vitello said, referencing Fenway. “But that was more of his ambition.” The Giants will reevaluate Mayer next week, with the hope that the foot soreness subsides and he can begin integrating into the major league lineup. For now, the team must wait, and the Fenway debut remains a tantalizing what-if.