Rafael Nadal says it is 'impossible' to win a Grand Slam if you have a genuinely serious injury, and you only risk doing further damage.
The Australian Open has seen a spate of abdominal injuries this year, with world number one Novak Djokovic currently fighting on despite a clear problem.
On Monday, world number ten Matteo Berrettini and Casper Ruud were both forced to withdraw with similar injuries, and Alexander Zverev has also had a problem during the tournament.
It has been speculated the the two week quarantine period is responsible for the injuries but Nadal, who came into the Australian Open with a back problem himself, has warned rivals they may be doing some real damage by playing on.
"It depends what kind of injury you have," Nadal said after his win over Fabio Fognini.
"You have something broken [or] a strain of your abdominal, for example... I did it in the past, and you make mistakes because it's impossible to know exactly what's going on when you are competing.
"For example, I remember in the US Open 2009 that I started the US Open with a strain in the abdominal.
"I started with six millimetres or so of strain, lost in the semi finals against [Juan Martin] Del Potro, and I finished the tournament with 26 millimetres. Of course it wasn't a smart decision."
Asked whether he would advise players to try playing through the injury Nadal added it was all about weighing up the risk against the reward.
"Well, it depends what you have later after the US Open," he said.
"I feel that if I have to rest for one month or something, it was not a disaster for me.
"You need to find a balance, but of course at this point of my career, if there is a big chance to increase something very important, probably I will not play because for me the happiness is much more important than give me a chance to win.
"And, at the same time, if you are bad, you will not win. That's clear.
"If you really have physical problems, you will not win. If you have some pain and it's not putting you in a situation that limits you, the movements, maybe you can find a way.
"But when you really, really have an injury, it's impossible to win a tournament like this."
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