John McEnroe has urged Andy Murray to enjoy himself more when he's on court - something the American didn't do enough of.
McEnroe is famous for the verbal outbursts and tantrums that littered his career, with his confrontational on-court persona his signature.
However, the 53-year-old says that the self-directed anger that Murray at times exhibits is of concern to him.
"It would be helpful to see Andy be sort of, 'I want to be here and I'm loving this'," McEnroe is quoted as saying after a match at the Statoil Masters.
"I say it as an ex-player and someone who wished that I had done that a little bit more. One of the things that worried me is that he used to get so negative that not only would it turn himself off, but it turned off people watching him."
While Murray finally broke his Grand Slam duck this year by winning the US Open, McEnroe admits the Scot has his work cut out to add further Grand Slams to his collection in 2013, with a tough campaign expected.
"This is around the time something is going to give," said the seven-time Grand Slam winner.
"Roger is amazing, but he's 31. Rafa is the one we don't know about, he hasn't played for seven months.
"Djokovic has finished the last two years at No 1, but it wouldn't be unheard of for him to have a letdown, but if he won two Grand Slams it wouldn't be shocking either.
"Andy has set himself up for a big year, although he missed a few opportunities at the end of this season."
'If he doesn't take it up a notch he would be disappointed, but if he wins one major that would be a good year. They're not very easy to win.'