He sustained a bone bruise on his right foot and began to use a walking boot and crutches.
Yankee fans got the wind knocked out of them as if they were punched in the gut when they heard the news.
No one knows what the future will bring, but many believe that Robertson is the likely replacement who will fill the role of closer when New York Yankees legend Mariano Rivera decides to retire.
Over four seasons with NY, he has pitched 202 innings with a win-loss record of 14-6, 270 strikeouts and a 3.03 ERA.
Robertson showed some good signs on Monday, as he shed the walking boot and crutches for five minutes on George M. Steinbrenner Field and played catch.
Yankees manager Joe Girardi plans to see how Robertson's foot responds over the next three or four days, as they increase his physical activity.
He will require some treatment to get himself back into game shape, and Girardi is not willing to jeopardize Robertson's beginning of the season.
Robertson believes that he will be ready for Opening Day, assuming that he has no setbacks.
His injury appears to be minor, and if he doesn't suffer any setbacks, he should be back to optimal health fairly soon.
Yankee fans need to take a deep, cleansing breath. He'll be fine.