You cannot be serious — about John McEnroe’s tennis charity.

The former Wimbledon champ’s nonprofit, the Johnny Mac Tennis Project, promises to serve scholarships to “expose young athletes . . . to the sport of tennis” and touts its programs in city schools.

But the real beneficiaries are elite players on the junior circuit who are getting their lessons and travel costs comped at Sportime, the for-profit Randalls Island tennis club where the John McEnroe Tennis Academy is located.

Sportime started the Johnny Mac Tennis Project in 2011 to create a cash stream to subsidize its top players, whose lessons the tennis club had been providing at a discount in order to build its prestige, according to a Sportime insider.

“It’s really a scam,” said the insider. “All the money goes to the for-profit business. Now we get reimbursed for our good deeds.”

The Johnny Mac Tennis Project raised $266,826 in 2012, and $242,625 of that was lobbed to Sportime so it could fund lessons for 20 players, tax records show.

The “charity” was the brainchild of Claude Okin, the owner of the Sportime chain of clubs, and Mark McEnroe, the tennis champ’s younger brother who was the general manager of the Randalls ­Island Sportime club and president of the separately incorporated nonprofit, the insider said.

The source said that John McEnroe had to be persuaded to sign on and that he donated no money to the effort at its inception. He is on the nonprofit’s board of directors.

John McEnroe did not return a call for comment. A spokesman for Sportime said John had always supported the charity and has donated his time and artwork from his collection to benefit it.

Sportime opened its 20-court Randalls Island center in 2009. John McEnroe lent his name to its academy program in late 2010 and gets $750,000 a year to teach there. The charity was then founded in March 2011.

Mark McEnroe admits the charity was “set up to find the very best kids we could find.”

“In our efforts to build our academy, we wanted to find a way that we could pay our bills and train the best kids and at the same time expose lots of other kids — like the hundreds of kids who come here in our community program — to the game,” said McEnroe who is now Sportime’s corporate development officer.

But while those community programs are done in the name of the Johnny Mac Tennis Project, their cost is paid by Sportime. The tennis center’s pros teach the kids on Randalls Island or at local schools.

“We didn’t have a lot left over to offset those costs,” Mark McEnroe said.

Three East Harlem youngsters got Sportime scholarships through the charity’s community outreach programs, but they were doled out only in the last six months.

In 2012, the nonprofit spent $45,470 to buy tickets to a World Team Tennis program featuring John McEnroe and resold them as its main fund-raising event.

This year’s Aug. 21 fund-raiser features current star Novak Djokovic and tickets go for up to $500.

Among those who have benefitted from the fund-raising is Noah Rubin, the 18-year-old Rockville Centre, LI, player who just won the junior title at Wimbledon.

Rubin received $32,200 from the Johnny Mac Tennis Project in 2011 alone, records show.

Jamie Loeb, the 19-year-old national college player of the year from Ossining, was pursued by John McEnroe and given a scholarship by his charity when she signed on to his academy in 2011, said her mother, Susan Loeb.

“They offered her a full ride,” she said.