Jax was diagnosed with a back contusion following his removal from Tuesday's game against Baltimore, Marc Topkin of the Tampa Bay Times reports.
Jax was hit on the back by a 107.2-mph line drive in the second inning and was pulled when the Rays took the field for the third. His diagnosis suggests that he didn't suffer any structural damage as a result of the incident. However, the team will likely keep an eye on him over the next couple of days before confirming him for his next start -- tentatively slated to come against the Tigers on Monday.