Frank Francisco's sore left hamstring isn't a major concern yet for the Mets, but the team was taking no chances by making the closer unavailable for last night's game against the Astros.

Manager Terry Collins indicated dehydration, stemming from the Denver altitude — the Mets just finished a weekend series at Coors Field — was the cause of Francisco's hamstring discomfort, which started Saturday.

But Francisco, who surrendered home runs in consecutive appearances against the Rockies, had another explanation for the soreness.

"It's from getting my [butt] tagged," Francisco joked before the Mets' 4-3 loss at Minute Maid Park.