General manager Brian Cashman told ESPN New York that Robertson, who had been New York's first choice to replace injured Mariano Rivera as closer, is expected to be out at least until the middle of June.
"They are all guessing games," Cashman said. "If it is sooner, great. If it is later, then it is later.
"If you are trying to iron me down right now, I would say mid-June. He hasn't had any setbacks in the last 48 hours."
The 27-year old is rehabbing at the Yankees' spring training complex in Tampa, but still hasn't begun bullpen sessions, simulated games or rehab games.
"None of that has happened yet," said Cashman, who typically is cautious with injuries. "He didn't think this was a serious issue and then the next thing you know, it turned into a DL and it has turned into something that is longer than 15 days."
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