MIAMI -- Dodgers setup reliever Jonathan Broxton was unavailable for Tuesday night's game against the Marlins because of a strained latissimus dorsi, the wing-like muscle in the upper back that stretches under the arm.

The reliever is listed as day-to-day.

Broxton tried to throw in the outfield Tuesday afternoon, then left Dolphins Stadium to have an MRI on the muscle, which is involved in the rotation of the shoulder during the throwing motion.

Broxton told the club he first felt the injury Sunday, when he pitched one inning and walked two during the eighth inning of the 3-2 win over Colorado. He reported it to team trainers on Monday.

The hard-throwing 23-year-old right-hander has a 2.31 ERA in 11 appearances with 16 strikeouts in 11 2/3 innings and a .190 opponents batting average, but he also has issued six walks. This is his third Major League season and he has never been on the disabled list.

Manager Joe Torre said Broxton told trainers he felt better on Tuesday than he did on Monday.