"It's not what you want, but you've got to figure it out," Girardi said. "Other guys will get a chance to step up. You expect them to step up and get the job done in his absence. We've had to deal with things like this before. We just need guys to step up."
In Robertson's absence, Girardi said that his first call will likely be to right-hander Shawn Kelley, depending on where the opponents' lineup is. Kelley set down Baltimore in the ninth inning on Monday to record his first career save.
"It forces all of us to throw another inning later, so obviously, that's not good for the whole 'pen," Kelley said. "But injuries are part of it, and we've got to overcome it. You saw today what we're capable of, and hopefully we can string it together until he gets back."
The Yankees promoted left-hander Cesar Cabral on Tuesday morning to replace Robertson on the active roster.
"Opportunity presents itself all the time," Kelley said. "I would give anything for David not to be hurt right now, because I know he's upset. We're a better team with D-Rob. But like I said, we've got to move forward, and we've all got to step up and fill some bigger roles."
Robertson said that he felt the injury while closing out Sunday's 6-4 win over the Blue Jays in Toronto, when he pitched around a hit and a walk to log his second save of the year.
"It just started aggravating me; I thought it was going to go away," Robertson said. "I had some pain in the afternoon, coming home on the flight, and this morning when I woke up, there was still some irritation there, so I came in and said something."
An MRI exam taken on Monday morning in New York revealed the strain. Robertson said that he believes he will be able to return in the minimum 15 days, but the timing of the injury is an annoyance that recalls a previous incident in his career.
Back in 2012, when Robertson claimed the closer's role following Rivera's season-ending knee injury, Robertson made just four appearances before he also landed on the disabled list with a strained oblique muscle. Rafael Soriano claimed the closer's job at that time, keeping it for the rest of the year.
"It's definitely a little frustrating," Robertson said. "It seems like something always happens to me. There's nothing I can do about it. There's no way I'd be able to go out there and be 100 percent, and do what I do the way I'm feeling right now."