GREENWICH — The athletic facilities at Greenwich Country Day School are due for a major expansion, thanks to the generosity of NBA star Donovan Mitchell, a former student.

The school administration is seeking approvals from the town Planning & Zoning Commission to construct a gym and basketball court with 53,596 square feet of new space at the independent school. The new athletic center would be built at the main campus at 401 Old Church Road.

According to the application filed recently with the town Planning Department, the Greenwich Country Day would demolish a section of the old athletic facility, known as the “small gym,” and put in a new basketball court in its place. The new facility would be a National Collegiate Athletic Association, or “NCAA-regulation sized basketball court,” according to Bruce Cohen, the attorney representing the application.

The independent school, founded in 1926 as an elementary and middle school, added grades 10th through 12th when it acquired and merged with the Stanwich School in 2017. It has been building out its athletic facilities since then, and the upper school basketball team has been competing with other private school teams in the region since high-school students were admitted.

Mitchell graduated from the ninth grade at Greenwich Country Day in 2012, and he and his family in December 2020 pledged $12 million to his alma mater. The donation was earmarked to fund the construction of the new athletic center, as well as provide support for student scholarships and a faculty recognition program.

The plan calls for the demolition of 7,260 square feet of existing space to make way for the new athletic center. The application has yet to be scheduled for review by the Planning & Zoning Commission.

When the gift was announced, Head of School Andrew Rohdie called Mitchell “a man of the highest character,” who lived up to the school’s ideals.

“I know how lucky I have been to have the foundation of my education happen here at Country Day,” Mitchell said when he made the donation. “This school has shaped who I am in so many ways, and I feel blessed to be able to give back and make the Country Day experience available for more kids especially those from inner-city neighborhoods or with backgrounds like mine.”

Mitchell’s mother, Nicole, taught at the Lower Elementary School at Greenwich Country Day from 2007 to 2019. His Mitchell’s sister, Jordan, graduated in 2017.

A three-time NBA All Star, Donovan Mitchell plays for the Utah Jazz, although there have been trade talks in recent days.

Mitchell, 25, grew up in Westchester County, N.Y. The 6-foot-1 guard earned a scholarship to the University of Louisville. He declared for the NBA draft in 2017 and was selected with the 13th pick by the Denver Nuggets, but was quickly traded to Utah Jazz, where he has played since.

Just before Thanksgiving 2020, Mitchell signed a five-year rookie extension with the Jazz that would guarantee him at least $163 million.

Besides Mitchell, GCDS is also noted for other famous alumni: former President George H. W. Bush; presidential press secretary Jen Psaki; Olympic hockey player Helen Resor; and Cameron and Tyler Winkelvoss, Olympic rowers and social network executives.