He was already considered raw and a bit of a project as a fifth-round pick out of Division III Albion, so spending his entire rookie season on the physically unable to perform list was a tough blow.
He practiced with the team for a three-week stretch midway through the season, but it wasn't enough to get him off PUP and onto the active roster.
"He just wasn't 100 percent," Detroit Lions general manager Martin Mayhew said of that short practice stint. "I talked to him about it. The trainers talked to him. He really wasn't 100 percent and he's a guy that needed some development, we knew that.
"To try and force the issue with him and activate him, we didn't know what we were going to get out of him anyway. He wasn't full go."
The Lions still have an opening at cornerback opposite
At last month's NFL Scouting Combine, Mayhew said Bentley, Green and Greenwood all had "starting potential."
Greenwood's length, athleticism and speed drew the Lions in last offseason. At 6-foot-1, 193 pounds, he fits the profile of what they're looking for.
He hasn't played any real football for 496 days from today's date, though. Greenwood seems to be a wildcard for the Lions in 2013. If he's as good as they think he's going to be, they're in pretty good shape in their secondary.
The Lions can't be sure how ready he is to contribute in 2013 until offseason workouts, OTAs and minicamps begin, but they seem optimistic.
"I have high expectations for him," Mayhew said of Greenwood. "I wouldn't describe him as a wildcard. He's a very talented young guy. He's going to benefit from having a full year in the NFL -- training room, weight room, what he's doing in the offseason.
"He's training right now with a personal trainer and working on football stuff. I'm looking forward to seeing him work this year."
Greenwood will be one of the more intriguing storylines early in the offseason training program and will have a lot of eyes on him.