BOSTON — Rafael Devers is the biggest story at Fenway Park this weekend, but for a few days the Giants anticipated another return being an intriguing undercard.The hope was that Marcelo Mayer would make his Giants debut against the team that traded him away on deadline day, but Mayer’s rehab assignment has been halted. The infielder is dealing with soreness in his right foot related to an injury he suffered while with Boston and the Giants will have him rest all weekend back in San Francisco.

Mayer had an MRI and CT scan that revealed the bruise. The Giants will reevaluate him next week.

“He just aggravated it a little bit from being back out there every day,” manager Tony Vitello said. “He’s just going to take the weekend off and then kind of reassess things later.”

The 23-year-old was 6-for-17 in four rehab games with Triple-A Sacramento. When the Giants acquired him, Mayer was on his way back from a stress reaction in his forearm, but he hasn’t had any issues with that in recent days. Now it’s about waiting for the foot soreness to clear up.

The Giants initially hoped to get...