If he actually used a medical his first year, he'll probably be considered a senior. DI rules are a lot more strict, especially with the 4 in 5 rule. If a student-athlete is injured in DI, it seems (at least watching NDSU's situation) that the NCAA requires the student-athlete to use up their redshirt season first. If the redshirt was already used, they may or may not grant a medical redshirt, but it seems like it's more often not. NDSU had more than a couple student-athletes lose a year of eligibility due to the difference in medical redshirts between DII and DI.
FWIW-real world example for UND fans would be the OL from SDSU that transferred to UND a year or two ago. His eligibility was gone in DI, but he could still play in DII.