​BOSTON — For weeks, Red Sox slugger Willson Contreras has been battling a balky left hamstring. On Monday, the issue became too much for him to continue to play through.Before Monday’s game against Seattle, Boston placed Contreras on the 10-day injured list with a left hamstring strain and recalled Mickey Gasper from Triple-A one day after sending him down as part of a roster crunch. Contreras, who departed Sunday’s blowout loss early due to hamstring soreness, will be sidelined through at least September 9.According to interim manager Chad Tracy, the decision was made not because Contreras suffered a setback, but rather because the club wants to ensure he’s healthy for the final few weeks of the season. As of Monday, the Sox have 24 games left in the regular season, which ends September 27.“I don’t want to paint the picture that something way worse happened. Just a recurring of the same thing,” said Tracy. “The thought of continuing down this road of trying two days (off) or three days (off) and you’re playing shorthanded, it just became apparent to give it the time it needs to heal. We didn’t have a huge setback or anything as far as where it’s been, so I’m hopeful that it’s that amount of time and we get him back and he’s able to play the game full bore like he likes to do.”Contreras has been open about his hamstring issue, which has been present since early August, and on multiple occasions said he had permission from Tracy and Boston’s coaches to not run hard after being booed by the home fans at Fenway Park. The Red Sox have tried to unplug Contreras from their lineup here and there throughout the last few weeks, including last week when they held him out of their series finale in Miami. He left Sunday’s 16-1 loss to the Yankees in the seventh inning due to the discomfort returning.At the plate, Contreras has not been himself in recent weeks. In 23 August games (98 plate appearances), he hit just .217 with three homers, 12 RBIs, a .715 OPS and 26 strikeouts. On the team’s road trip to Miami and New York, Contreras was 3-for-23 (.130) with a triple and seven strikeouts.“We’re just to the point where you know, ‘If we need to give him another few days to let it calm down, we’re getting to a point where it’s tough to be short bodies,” said Tracy. “Need the bat with Mickey. It’s to the point of, ‘How do we do this and get completely over the hump and let him have the rest he needs to get him healthy so he’s with us for the final push?’”Contreras has started 123 of Boston’s first 137 games at first base but the club will now turn to depth options for at least 10 days. Gasper will play there Monday, marking his third start of the season at the position. Nick Sogard can also play first, as can Andruw Monasterio and Isiah Kiner-Falefa (who is very likely to be activated from the IL on Tuesday when rosters expand to 28 players).Gasper’s return to the majors comes one day after what Tracy