Pancho Segura taught tennis to the Hollywood crowd for many years. Will ask him about Mickey Rooney. Asked him who stood out he said this (link here):
Tennis Week: I’ve read and been told Errol Flynn was one of the best tennis-playing Hollywood stars. You taught tennis for so long out there, who was the best celebrity player?
Pancho Segura: I used to play with Flynn he was pretty good. Dino Martin, Dean Martin’s son, was good and so was Vince Van Patten. They were probably the best celebrity players. Chuck Heston was good. He once said he’d rather play tennis than make love. I don’t know if I could go that far (laughs).
I knew someone who hit with the young Katherine Hepburn and was told she was a very good athlete, and a solid, but not great, tennis player. Also, Joel Drucker wrote a good piece about Hollywood tennis players, if I can find it somewhere will try to post it. From what I remember, Groucho Marx and Charlie Chaplin were both avid players, according to that Joel Drucker piece. Can't remember their level of play. Dustin Hoffman is an avid player, but I have never seen him play so have no idea his level. From what I remember from his story, Jack Nicholson, while not a technically trainer player, was so competitive and such a hustler he was competitive. In the Pancho Gonzalez documentary they interview Robert Redford, who was apparently a fine junior in California (he went to college on a baseball scholarship and told ESPN he hit a ball out filming The Natural so he must have been good). Never saw Metallica drummer Lars Ulrich play but have been told he was really good too (Torben Ulrich's son). People have told me Gavin Rossdale is very good.
I knew a guy who coached at Harlem Tennis Center for years and he told me Earl Monroe played up there for years (prior to his last knee surgeries) and he described him as a quick serve and volleyer. I know Joe Morgan did play tournaments at one time and was apparently pretty good - he was such a good hitter have to think he would be very good tennis player.
Obviously John Lucas played college and was very good (again never saw him play). My friend is a teaching pro and he saw both Brady Anderson and Paul O'Neill play and said both were good players, especially Brady Anderson. I've read that Jim Palmer (hall of fame pitcher) taught himself to play lefty so he would not risk injury to his arm. He looks like he'd be good. Anna Wintour, who is frequently in Federer's support box, apparently plays 2 or 3 days a week early mornings in NYC, but have no idea her level. I was told Chris Mad Dog Russo is a good solid player too. Carlos Santana, Robert Plant, Elton John, Boyd Tinsley all play pretty regularly from what I am told, but no idea about their level.