John McEnroe believes Nick Kyrgios gave tennis a bad look following his fourth-round exit from Wimbledon at the hands of Andy Murray on Monday.
Kyrgios went down in straight sets to world number two Murray, despite looking up for the challenge in the opening stages of the match.
However, after narrowly losing the first set, Kyrgios conceded he "lost belief" from that point onwards, eventually going down 7-5 6-1 6-4 in well under two hours.
McEnroe - a seven-time grand slam winner - claimed Kyrgios was only giving "80 per cent" against Murray, and believes the 21-year-old must change his attitude to the game if he wants to succeed.
"Boy, I expected Murray to win, but not in one hour and 39 minutes," he said. "This is not doing our sport any good.
"What's he's giving, 80 per cent? This is Wimbledon, centre court. You've got to give 110 per cent to try to get back into it.
"It's not just the mental part, he needs to work on his game. He doesn't know what it takes to be a top-10 professional to win grand slams.
"I'm hoping he sees the writing on the wall before this becomes chronic, irreparable, because to me it's getting to that point.
"He's got a lot of thinking to do, a lot of work to do."
McEnroe added: "He's got to look in the mirror if he wants to become a top player and win slams. Based on that performance, I'd become more concerned.
"I still think he is going to win slams, but not in the way he played there."