With Kyler Murray declaring for the NFL draft, Tim Hasselbeck explains how size expectations for quarterbacks have changed in recent years. (1:22)

Kyler Murray has elected to enter his name into the NFL draft, announcing the decision on Twitter on Monday. Editor's Picks Is Kyler Murray now locked into football? Answering every question

Ranking best NFL fits for Kyler Murray: Where the QB could thrive

The plays that helped turn Kyler Murray into an NFL prospect 2 Related

The Oklahoma Sooners quarterback and reigning Heisman Trophy winner has given himself the option to choose the NFL over Major League Baseball, for which he has a contract with the Oakland Athletics that includes a $4.66 million signing bonus.

A source told ESPN's Adam Schefter that Murray actually submitted the paperwork Friday.

The A's, who selected Murray with the ninth pick in the 2018 MLB draft, understood and supported his decision to enter the NFL draft, sources told ESPN's Jeff Passan.

The choice to enter the NFL draft does not preclude Murray from choosing baseball, sources said, but it does put additional pressure on Oakland to offer Murray a major league contract with additional money in hopes of dissuading the outfield prospect from pursuing a football career.

Top A's executives, a marketing executive from MLB and others met Sunday afternoon with Murray in Dallas, sources told Passan, to better understand what it would take for Murray to forgo a football career and to sell him on playing baseball full time.

play 1:57 Schefter: Murray will go in first round Adam Schefter joins SportsCenter to analyze Kyler Murray's decision to declare for the NFL draft.

Both sports have key dates next month. Players must report to the A's for spring training on Feb. 15. The NFL Scouting Combine begins in Indianapolis on Feb. 26, with the NFL draft taking place on April 25.

ESPN's draft experts, Mel Kiper and Todd McShay, both project Murray as a first-round pick. Kiper says, "He's unbelievably athletic and one of the best dual-threat quarterbacks I've ever seen. He can make every throw, and he does it with timing, touch and poise. He could be a really good NFL quarterback."

If Murray were 3 inches taller, Kiper predicts he would be the No. 1 overall pick. But at 5-foot-10, he would be the shortest quarterback in the NFL since Doug Flutie.

In just his first season as a starter at Oklahoma, replacing Heisman winner and No. 1 draft pick Baker Mayfield, Murray threw for 4,361 yards and 42 touchdowns and ran for another 1,001 yards and 12 touchdowns in leading the Sooners to the College Football Playoff semifinals this year.

Although Murray has entered his name into the NFL draft, he still has 72 hours during which he can chose to pull out.

Next stop, NFL? Sooners QB Kyler Murray has announced he's entering the draft, but a future with the Oakland A's remains a possibility. Kevin Jairaj/USA TODAY Sports

NFL teams get the rights to players for only one year. There is no draft-and-stash process like there is in the NBA. So if a team drafts him and Murray doesn't sign, that team loses his right after a year.

Pro Football Hall of Famer Deion Sanders, who played in both the NFL and MLB during his career, knows what he would do if he were Murray.

"If I was in his shoes, I'm picking up the baseball bat and I'm not looking back," Sanders told ESPN.