Ivan Lendl is a hard man.

As Andy Murray prepares to play his semi-final here at the French Open today against Stan Wawrinka, the former world No.1 believes the Scot struggled in the first half of the season not because he didn’t have enough rest but because the pair were not able to work hard enough in the off-season.

It was Murray’s stunning second half of 2016, of course, that took him to the world No.1 ranking for the first time, another of his career goals ticked off.

But that outstanding effort meant he needed rest and, combined with his father’s wedding, Murray and Lendl worked together less than they wanted, or at least less than Lendl thought was ideal.

“We did 17 days so we had to move around one or two days because of rain-outs,” Lendl said yesterday.

“I just feel that we could have used another week, because then you can put more work in, you can work on more patterns, you hit more balls.

“When you come from the off-season you just need to hit a lot of balls, you have to get a lot of repetition. I just thought it was unfortunate it was that short, I could have used another week.”

It was in Australia where things began to go wrong, his early defeat by Mischa Zverev of Germany an indication that perhaps the previous 12 months would take their toll.

Shortly after arriving home, he revealed he had been diagnosed with shingles, something Lendl said explained his performances in Melbourne.

“Nobody knows how exactly that comes around, why that comes around, how long is it in your body before,” he said.

“Andy was telling us he feels sluggish in Australia and we saw absolutely no reason why he is feeling sluggish, then he goes home and three days later he texts that he got shingles.

“You talk to a doctor and he will tell you that it is in the body 2-3 weeks in advance, maybe that is why he was sluggish.”

He won the title in Dubai but then pulled out of Miami with an elbow injury and had flu straight after.

Those things meant that his preparations for the clay-court season were shorter than usual and he was unable to train with Lendl in Miami.

The pair were reunited here a week before the start and Murray has shown a vast improvement in his game at Roland Garros, reaching the semi-finals for the fourth straight year.

For the second year in a row he will take on Wawrinka for a place in the final and he’ll be hoping for a repeat of what happened 12 months ago when he beat the Swiss with one of his best ever performances on clay.

“You have to put in consistent work to have consistent results,” Lendl said. “If you have three illnesses and an injury which take you out for some time, you start again, you get going and you get ill or injured again, then you start again and again and again.

“It’s very difficult mentally for the player. It’s nice that Andy’s healthy and he can put the practices in and I think the results are starting to come.

“With the exception of the first two or three days, when he had a bit of flu, he has been putting in great work. He scraped through the first two matches and then the work started to come in.”

Lendl said he didn’t feel Murray was yet playing the kind of tennis he did in 2016 but that he is on the right track.

He showed good resilience about being outplayed by Kei Nishikori in the first set of their quarter-final, evidence that he is finding a way to win even when not playing his best.

Wawrinka, the champion in 2015, has not dropped a set here this fortnight but Lendl brushed away a suggestion that the fact that the Swiss has not been tested could play into Murray’s hands.

“I always read that you need a tough match early to get through it and that if you go through the draw without losing a set it may hurt you, but I kind of chuckle at that,” he said.

“I don’t really pay much attention to that. As long as you have enough left in the tank it’s OK.”

The other semi-final sees the nine-times champion, Rafael Nadal, taking on the young Austrian, Dominic Thiem.

Thiem should have plenty of belief after ousting defending champion Novak Djokovic in the quarter-finals but this is Nadal, who is oozing confidence after cruising through his first five matches.

It promises to be long, punishing, gruelling, physical and mentally exhausting and in the end, it would be a big surprise if Nadal does not find himself in a 10th French Open final.