Roger Federer offered stuck-at-home amateurs the ultimate online fantasy camp of sorts, a chance to get tennis tips from a guy many consider the greatest of all time.

While people all over the world are cooped up because of the new coronavirus — social distancing while trying to stay healthy and help others do the same — a bunch of athletes have been posting workouts and drills on social media with suggestions for staying in shape.

Federer did that sort of thing, too, with what he called “a helpful solo drill,” but he also took it a step further today: He encouraged folks to tweet to him their own videos mimicking the volleying exercise he displayed. And then he replied to some, even dispensing a little advice.

Not a bad instructor, eh?

The owner of a men’s-record 20 Grand Slam singles titles previously posted clips of himself hitting against a wall in the snow, including around-the-back or through-the-leg-‘tweener trick shots.

This time, the 38-year-old Federer donned an all-white outfit — perhaps a nod to Wimbledon, the grass-court tournament he’s won eight times, which was canceled for 2020 last week? — replete with a white panama hat with black band, stood near the green wall and volleyed against it.

He tapped the ball more than 200 times during the test of reflex and form in the 59-second video.

Within six hours, Federer’s clip garnered more than 1 million views, and his post drew more than 1,300 replies.

True to his word, he answered some.

“Don’t lean back, strong in the wrist,” Federer wrote to one person. “Keep up the great work.”

To another, in which a man hit a tennis ball against an indoor wall while a dog appeared to nap underneath, Federer answered: “Love the confidence not to drop the (tennis ball emoji) on the (dog emoji).”

To others, he sent verbal pats on the back, such as, “Good job” or “Nice work” or “Love the effort.”

Federer, who had arthroscopic surgery on his right knee in February, is waiting along with everyone else for competitive tennis to return. The men’s and women’s professional tours are suspended until at least mid-July because of the COVID-19 pandemic.

The U.S. Tennis Association issued advice last week to avoid playing the sport with anyone else right now, calling it “in the best interest of society to take a collective pause.”

The USTA noted that there is “the possibility” that germs could be transferred among people via sharing and touching of tennis balls, net posts, court surfaces, benches or gate handles.

More than 1.3 million people have been confirmed infected by the coronavirus around the globe, and more than 75,000 have died, according to Johns Hopkins University. The true numbers are almost certainly much higher, because of limited testing, different rules for counting the dead and deliberate under-reporting by some governments.

For most people, the virus causes mild to moderate symptoms such as fever and cough. But for some, especially older adults and the infirm, it can cause pneumonia.