Jennings’s decision, driven by circumstance and opportunity, is challenging the custom that an elite player must attend college before he pursues his dream of playing in the N.B.A. Playing professionally in Europe suits Jennings’s basketball goals and is far more lucrative than a college scholarship. He was an all-American at Oak Hill Academy in Virginia and was considered the nation’s top point guard.

No one knows the effect that a parade of elite players taking Jennings’s path would have on the college game, and the flow of players to Europe is expected to be a trickle rather than a flood. The N.C.A.A. tournament has thrived even though a generation of stars like Kevin Garnett, Kobe Bryant and LeBron James skipped college for the N.B.A.

“I don’t know what’s going to happen in terms of other people,” Myles Brand, the president of the National Collegiate Athletic Association, said in a recent interview. “But I would hope and expect that most would want to go to college, not just to play basketball but to get an education.”

David Stern, the N.B.A. commissioner, is an advocate for having high school players wait a year to enter the league. He said that Jennings would probably have a better basketball experience in Europe than in college. N.B.A. teams have sophisticated scouting systems abroad, Stern said, and 74 international players began last season on league rosters.

“I actually think it’s a pretty cool thing for a kid to do what he’s doing,” Stern said. “There’s a big world out there. If you want to play for Rome as opposed to Arizona, go ahead and do what you think is best. It’s a positive development for kids and for the N.B.A. scouts.”

At lunch near the Pantheon, Jennings spun fettuccine Alfredo on his fork and referred to playing college basketball several times as “the easy road.” Jennings said he regretted that he did not declare his intentions to play in Europe before he left high school. He said he would have received a bigger contract and shoe deal if there had been more hype.

Instead, Jennings, an admittedly apathetic student, signed a letter of intent to attend Arizona and planned to stay there only one season. But he struggled to reach a standardized test score to meet the N.C.A.A. minimum for a scholarship. (He and his mother, Alice Knox, said that his last SAT score was questioned by the testing service and that they still had not received it.)