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The Tigers bullpen has been their Achilles heel all season. The bullpen's ERA is an AL-worst 4.86 so far this year.
In 126 innings, Tigers relievers are second worst in the league with an opponent batting average of .262 and have given up 60 walks, second most in the AL.
With the injury to starter Doug Fister and the inconsistency from Valverde, the bullpen has been pressed into extra work and unexpected situations.
"That's the one thing we've got to get synced," Leyland said to the Detroit Free Press on May 12. "I haven't really done a good job of that just yet. I think the key to that is Fister being back in the rotation. I think we will get that ironed out now."
Valverde has been sidelined since leaving the game against on May 16 against the Chicago White Sox in the ninth inning with back issues, but he remains on the 25-man roster.
To help replace Valverde, the Tigers recently recalled Brayan Villarreal, giving Detroit eight relievers instead of their normal seven.
Villarreal has taken advantage of his opportunities in his second year with the team, giving up just two hits in six innings of work this season, without being charged with an earned run.
But Collin Balester and rookie Luke Putkonen remain in the bullpen, despite Putkonen allowing seven runs in six innings of work (10.52 ERA), and Balester's 6.50 ERA in 18 innings. The two have combined to give up 16 walks in 24 innings.
To help the bullpen, the Tigers have been hustling along Luis Marte, who's been on the disabled list since Detroit's last spring training game, in which he strained his hamstring.
Marte debuted with the Tigers last season, throwing 3.2 innings, giving up one run (2.45 ERA). He was 2-0 with a 2.08 ERA in nine Grapefruit League appearances this year.
He began this season with an injury-rehabilitation assignment on May 17 for Single-A Lakeland, throwing two scoreless innings. He was later transferred to Toledo.
Marte shined again on Monday, throwing three scoreless innings for Toledo, giving up just one hit and one walk, while striking out two batters.
Leyland said Marte could return to the Tigers on Friday in Minnesota, which would likely mean a Triple-A demotion for either Balester or Putkonen.
Because Detroit only has 12 position players on its 25-man roster, Marte's eventual call-up could prompt the Tigers to option another reliever to Triple-A, meaning both struggling relievers would likely be sent down.