For the past several years, Billy Donovan's jump to the NBA has seemed inevitable. But anticipating it happening doesn't lessen the blow to college basketball.

Donovan on Thursday agreed to a five-year deal to become the head coach of the Oklahoma City Thunder, league sources told Yahoo Sports. This is a huge loss to a fragile game. It's an understandable move for the man, but a detrimental outcome for the wobbly sport he's leaving behind.

Donovan is on the very short list of the best coaches in college hoops – has been for a while, and could have been for another 15-20 years if he had chosen to stay at Florida. Every bit as significant is what he means to his peer group and his conference.

View photos Billy Donovan took the Gators to four Final Fours. (AP) More

In former Butler coach Brad Stevens and Donovan, college basketball has lost its last two coaches under 50 who have made multiple Final Four appearances. Donovan is barely under that wire, turning 50 in late May, but the point remains that the top of the college coaching profession is not getting any younger.

Since Donovan won his second consecutive – and last – national title in 2007, five of the coaches who cut down the Final Four nets have been 58 or older: Roy Williams in 2009; Mike Krzyzewski in 2010 and '15; Jim Calhoun in '11; and Rick Pitino in '13. Average age of the championship coach since '07 is 58 years old. This year's national championship game pitted 68-year-old Mike Krzyzewski against 67-year-old Bo Ryan, and the average age of the 2015 Final Four coaches was 63.

There are some bright lights among the younger generation, notably 42-year-old 2014 national title winner Kevin Ollie of Connecticut and 38-year-old new Texas coach (and former Donovan assistant) Shaka Smart. But in a sport where there is concern about having enough up-and-coming quality coaches, losing two superstars like Stevens and Donovan hurts.

Stevens' success in two seasons coaching the Boston Celtics has only helped clear the way for Donovan – and perhaps others in the future. Ollie was a reported secondary candidate at Oklahoma City if the Donovan deal did not work out. Kentucky coach John Calipari took a long look at the Cleveland job last year, and those who know him have long said that he has an interest in returning to the league where he failed in the 1990s.

Brain drain in a sport that is struggling to identify its next generation of star coaches is a significant issue.

Donovan is one of the most important figures in the modern era of college basketball. As a player on the Final Four Providence team of 1987, Donovan helped usher in the 3-point shot as a major strategic weapon. As a coach he had huge accomplishments at a young age: taking over his first program (Marshall) at 28; moving to Florida at 30; winning his first title at 40; his second a year later; and chalking up 502 victories before age 50.

The other negative impact of Donovan's departure is on the Southeastern Conference. A strong case can be made that Donovan is the second-greatest coach in SEC history, behind only Adolph Rupp.

Rupp won four national titles. Donovan won two. Nobody else in the history of the league has won more than one.

Donovan's four Final Fours also is surpassed by only Rupp, who had six. Calipari also has made it to four as coach at Kentucky. Nobody else has made more than three as an SEC coach.

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