In December, Oregon quarterback Marcus Mariota was presumed to be the top pick in the NFL Draft by the Tampa Bay Buccaneers. Three months later, Florida State quarterback Jameis Winston is expected to be the top pick and Mariota has become the draft's biggest mystery.

First there was Mariota's poor performance in the college football championship game against Ohio State. Then there were knocks on his ability to run a pro-style offense and questions about whether he can even call a play in a huddle, something he was not asked to do at Oregon.

Then, the final straw for some, was a ho-hum pro day workout which Dan Brugler of CBSSports.com said "wasn't impressive" and was described as "underwhelming" by Rich Cimini of ESPN.

This has led to speculation that Mariota could slide on draft day much further than many people would have imagined just a month ago.

Previously it was thought that Mariota would not fall past the New York Jets who have the No. 6 pick. But Peter King of theMMQB.com is now wondering if Mariota will still be available much later:

"What if Mariota—and this is a huge “what if” because of all the teams that need quarterbacks in the draft this year—starts to tumble down the draft board in round one? What if Washington passes on him at 5, and the Jets have some cold feet at 6, and GM Les Snead of the Rams loves Nick Foles and sees bigger needs at 10, and the Browns at 12 and the Texans at 16 and the Browns again at 19 all have cold feet for one reason or another? All of those things are incredibly unlikely, but what if? What if Mariota is staring Sam Bradford-loving Chip Kelly in the face at 20, or if Kelly sees Mariota tumbling at 12, 13, 14, and he thinks he’s just got to go for the gusto now?"

There appear to be three key teams that will determine where Mariota will be drafted:

1. Tennessee Titans (No. 2 pick) — The Titans have not ruled out the possibility of drafting a quarterback. King was recently told not to discount the Titans picking Mariota and that they are "very serious here." Still the Titans have shown support for second-year quarterback Zach Mettenberger and most experts feel the Titans will pass on picking a quarterback unless Winston is still available as he would seem to fit their style of offense better. Of course, the Titans could also be feigning interest in Mariota to drum up the price of trading the pick, which could be the smart move if they really do prefer Winston and can't get him.

2. New York Jets (No. 6 pick) — The experts think this is the most likely spot for Mariota to land. But that assumes no trades and, if true, a team that really wants Mariota will have to jump ahead of the Jets into one of the top five spots. In addition, if the Jets are interested in Mariota, they could swap picks with the Titans, which would guarantee they get Mariota and allow the Titans to remain in the top six while also adding a valuable draft pick or two in the trade.

3. The Philadelphia Chip Kellys (No. 20 pick) — Of course, the wild card is Chip Kelly and the Eagles. Kelly, who coached Mariota at Oregon, recently called his former pupil "the best QB in the draft" according to Lorenzo Reyes of USA Today, but he vowed not to mortgage the team's future to get him. The speculation is that the Eagles would have to trade the best parts from their next two drafts in order to move up from No. 20 to No. 2, a monumental leap in the NFL. However, the Eagles also have the the recently-acquired Sam Bradford as leverage to trade up, something some NFL coaches are still convinced will happen according to Josina Anderson of ESPN.

View photos Jameis Winston and Marcus Mariota More

Of course, now add in the reaction by some like King that both the Titans and Jets could pass on Mariota and his stock may tumble.

Charley Casserly of the NFL Network was very unimpressed following Mariota's pro day, saying Mariota is "not a sure thing. If you’re going to take him, you’ve got to hold your breath."