Stephen Hendry was at a loss when asked who he thinks can challenge Ronnie O'Sullivan ahead of the World Snooker Championship.
O'Sullivan will be aiming to break the record of seven titles he shares with Hendry when he heads to the Crucible later this month.
The final tournament before the Sheffield event is currently taking place at the Tour Championship in Manchester.
O'Sullivan is aiming to win his sixth competition of the season and won his quarter-final against arch-rival Ali Carter on Wednesday.
Ronnie O'Sullivan left Stephen Hendry 'struggling for an answer' at the Tour Championship
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He was drawn against Gary Wilson in the semi-final after his fellow Englishman beat Mark Selby and Zhang Anda in the first two rounds.
Ahead of the clash, Hendry was asked by ITV's Jill Douglas who he thinks can stop O'Sullivan ahead of the World Championship.
And the Scot was unsure that there is anyone, responding: "That's a good question, it's a very good question.
"If I'm honest I'm struggling with an answer because he's brushing aside everyone he's playing really.
"What he does, even in the first round, for the first three or four frames against Ali Carter he missed the odd shot, the odd little mistake, sort of feeling out his opponent.
"As in boxing, a few little jabs in there and then he goes for the killer punch and just destroys them. He's got everything, hasn't he?"
Neal Foulds agrees with Hendry that there are not many players on the tour who can currently beat O'Sullivan.
Foulds says there is a mental aspect where some players become 'fazed' by playing the Rocket.
He said: "Who's going to beat Ronnie O'Sullivan? The question you asked.
"I think half of it is how brilliant a player he is, the best ever.
"And the other half is that a lot of players are very fazed by playing him and that applies.
"It applied when Stephen was at the top as well and occasionally they just don't play their best against the greatest."
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Stephen Hendry and Neal Foulds wonder who can stop Ronnie O'Sullivan
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O'Sullivan gave rare praise to his rivals ahead of the match with Wilson.
He said he was not surprised it has taken Wilson a while to reach the most successful point in his career due to the level of the tour.
O'Sullivan said: "Not really [surprised]. It's not easy, it's not easy to win tournaments, it's not easy to win quarter-finals of tournaments.
"It's a tough circuit, there's a lot of fantastic players there.
Ronnie O'Sullivan has already won five tournaments this season
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"Pretty much anyone can beat anyone of their day so sometimes you have to rely on a bit of luck that your opponent doesn't play well and you get through them matches and things pan out for you.
"Sometimes you need a little bit of luck and things to go your way."