Shafer was dealing with a flexor mass irritation during spring training and pitched in only one game in February, John Fay of The Cincinnati Enquirer reports.
Shafer was a long shot to make the Reds' Opening Day roster, having been acquired for cash considerations from the Jays after they had already designated him off their 40-man roster. The arm injury further limits his chances, though the delay to the start of the regular season could help Shafer log more exhibition appearances before Opening Day.