ALLEN PARK, Mich. -- Zach Zenner knows he might eventually have to make a decision. He's not thinking about it now as he focuses on trying to make the Detroit Lions as a reserve running back, but in the future, it's possible.

Zenner wants to be a surgeon whenever he finishes up in the NFL. So he applied to med school, was accepted to and then chose to attend the Sanford School of Medicine at the University of South Dakota, ranked tied for the No. 78 primary care medical school in the nation according to US News & World Report.

Football, though, became the priority, so Zenner asked for a one-year deferred enrollment to the school, which was granted.

"I explained that I want to pursue this NFL dream and at the same time I want to attend medical school," Zenner said. "I made my aspirations clear that I wanted to do both and they were flexible and said, you know, we'll go just on a year-by-year basis."

This doesn't mean a clock isn't ticking somewhat on Zenner's initial medical school plan. Paul Bunger, the dean of medical student affairs at the Sanford School, said he couldn't remember a case at the school where they granted more than a two-year deferred enrollment.

Bunger said there is a Feb. 1, 2016, decision date for whether a student will enroll at the school in July for 2016-17. While Zenner has already been accepted to Sanford and would have automatic admission should he enroll next year, Bunger said Zenner's application has to be in the AAMC database by November 2015 for him to enroll in July 2016.

Bunger said "almost all schools" would consider a second year of delayed enrollment if there was a reason for it. He said there was no precedent he knew about at Sanford beyond two years of delayed enrollment.

The other issue is how long the school will accept Zenner's MCAT score before he might have to re-take the test. Medical schools typically will consider scores valid between two and three years from the initial test, but it is up to the individual school how long it will honor that before retesting has to occur.

"Re-taking the MCAT would be a major step," Zenner said. "But a process I would definitely consider if things in the NFL are going well."

That is a long way off. Zenner, who is in a competition to be the fourth running back with George Winn and potentially Emil Igwenagu, still has to make the Lions or be picked up on a practice squad or another roster if he does not make the initial 53-man team.

Zenner heard the story of Kansas City offensive lineman Laurent Duvernay-Tardif, who has been balancing medical school and an NFL career. Zenner said he would be open to that possibility eventually once he had his NFL career in order.

That could be tricky at Sanford, where Bunger said he didn't know how someone could manage both.

"I can't imagine how anybody could do that," Bunger said. "I think NFL players, even though they have so-called offseason, they are busy. They have responsibilities and all sorts of things. It provides a very unique opportunity and that's what we look at as a policy for our delayed matriculation.

"Is it something that provides a unique opportunity for the student to further develop in an area that would give them some unique insight into people that they are going to care for some day."

Zenner said he doesn't know what type of surgery he would like to pursue, but that it is definitely something he plans on doing in the future. He doesn't have a timeline for when things will happen, mostly because he is focused on football now.

"You're working hard to try and make the NFL and that's one of my goals," Zenner said. "You know, despite there being a backup plan, I'm still working my butt off trying to make this team. There's not a sense of, well, I'll be OK afterwards.

"I'm working hard to make this roster. I know that is there, but I want to do this. And then, do that."