1. His size. You can be on the small side and still play Center in the NFL. However, being small limits his ability to switch to another position. Could he play OG in the NFL? Maybe. Could he play Tackle? Highly unlikely. One position means less value and limited upside. With a first round pick, teams want franchise players. Matt might become one, but doesn't seem to have that upside on paper.
2. Undervalued Centers. Few teams spend first round picks on Centers. Since 2000, only six centers have been drafted in the first round. Despite the Center's importance in picking up coverage, teams like to build around Tackles. Centers are often afterthoughts. Is Matt a big enough name or have enough upside to use a first round pick?
What can he do at the Combine help his draft status?
I don't think the Combine will change much about Tennant's status. I am sure he'll do well in the interviews. BC guys always seem to impress with their smarts, attitude and interview skills. But assume teams know about his personality already. To continue his momentum, Matt will need to blow teams away with his performance in the drills. A Mamula-like performance combined with interview skills and his tape would make it easier for a team to use a high-value pick on Tennant.
But being a Combine warrior has its downside too. Teams and fans expect too much. In the end, I think the second round might be the best solution for Matt. He'll have a chance to play right away and grow without the heightened expectations that come from being a first rounder.