Cardinals president of baseball operations John Mozeliak said Tuesday that Gray has been diagnosed with a "mild" right hamstring strain and it would be "challenging" getting the pitcher ready in time for Opening Day, John Denton of MLB.com reports.
Mozeliak referred to the news as "encouraging" on the whole, but Gray will need some down time and is not expected to be ready for what would have been his Opening Day start March 28 versus the Dodgers. Zack Thompson or Matthew Liberatore could fill Gray's spot in the rotation, and it's possible both will be needed if Steven Matz isn't quite ready.