The A’s expect Heisman Trophy winner Kyler Murray, the team’s top pick in June, to declare for the NFL draft Sunday, multiple sources told The Chronicle on Wednesday.

Declaring for the draft does not guarantee that Murray, an outfielder whom Oakland selected ninth overall, will decide to reject his $4.66 million deal with the A’s outright, but it certainly increases the chances that Oklahoma’s quarterback will decide to go pro in football rather than baseball.

According to a source, Murray declaring for the draft is not considered to be contractually significant.

Should Murray, 21, opt to enter the NFL draft, the real question will come Feb. 15 when A’s position players report to Mesa, Ariz. — Murray has an invite to big-league camp. He still could opt to be in the A’s camp, but the NFL scouting combine begins Feb. 26 and any high-round hopeful would be expected to attend. That’s when Murray would have to make a decision between football and baseball. One source told The Chronicle that Murray, a possible first-round NFL pick, is leaning toward football.

Late Wednesday night, a source indicated the A’s might consider allowing Murray to go the combine, a move that would require the approval of Major League Baseball.

If Murray chooses the NFL and does not play baseball, he would have to return the signing bonus, but the A’s will not receive a compensation pick in this June’s draft. Numerous first-round major-league picks have failed to sign, including Stanford pitcher Mark Appel in 2012, but the Pirates received a compensation pick the following year.

“That’s a huge problem, not getting a draft pick back,” one source said Wednesday evening. “That would be really bad.”

The A’s would retain Murray’s professional baseball rights should he join an NFL team, meaning he still could play for them if football did not pan out. Listed at 5-foot-10, Murray is short for an NFL quarterback, a concern for some teams. Still, his size would not necessarily preclude him from being selected in the first round nor from enjoying a productive career.

Murray’s draft outlook could weaken if he declared for the draft but did not attend the combine or NFL teams’ predraft workouts. There is, however, no possibility that Murray could play both football and baseball in the same year. Multiple sources agreed Wednesday that the demands of learning and playing quarterback in the NFL would preclude Murray from playing professional baseball at the same time.

Oakland’s deal with Murray allowed him to return to Oklahoma and play football for his junior season, which he did spectacularly. When he signed, the A’s and agent Scott Boras indicated that the agreement did not allow for him to return for his senior season.

Boras told The Chronicle in early December that his client planned to report to A’s spring training in February, but Boras softened that stance five days later.

What happened in the interim? Murray won the Heisman Trophy.

“When you win the Heisman Trophy, you’re going to have a lot of information come to you to be looked at,” Boras said at the winter meetings in Las Vegas. “All I know is Kyler has a tremendous opportunity to be a great baseball player and he knows that. … He has every intention to be in spring training and advance that interest.”

Susan Slusser is a San Francisco Chronicle staff writer. Email: sslusser@sfchronicle.com Twitter: @susanslusser