The Tigers had Nathan undergo an MRI yesterday, after he left a rehab outing with an injury.
The 40-year-old Nathan is in the second year of the two-year, $20 million deal that he signed with the Tigers prior to the 2014 season. Nathan had been coming off an excellent season with the Rangers, when he went 6-2 with a 1.39 ERA and 43 saves in 64.2 innings.
Nathan pitched in 58 innings last season with Detroit, saving 35 games in 42 opportunities. Despite decent save numbers, Nathan wasn't stellar like he had been in 2013, pitching to a 4.81 ERA and a 3.94 FIP, due to his uncharacteristic 54/29 strikeout-to-walk ratio.
This is not the first time in Nathan's career that he will undergo Tommy John, as he had the procedure with the Twins in 2010.
While the Tigers likely didn't see Nathan as the long-term closer this season, they probably hoped that he could contribute out of their bullpen. Detroit's bullpen hasn't been fantastic to start the season (ranking in the bottom third of the league in xFIP) and the loss of Nathan certainly doesn't help. They'll likely need to acquire a bullpen piece before the end of the season.