Sushi blamed for collapse of Andy Murray's father-in-law Nigel Sears

Nigel Sears collapsed while watching Ana Ivanovic's third-round clash with Madison Keys at the Australian Open. Darrian Traynor/Getty Images

Andy Murray's father-in-law Nigel Sears says he feels like a "fraud" after collapsing at the Australian Open -- because it was due to food poisoning and not, as originally feared, a heart attack.

Sears, coach of Ana Ivanovic, was watching the former French Open champion in her third-round tie against American Madison Keys on Rod Laver Arena when he blacked out.

Speaking to The Times, Sears said he "suddenly started to feel unwell as if I had eaten something which disagreed with me" while he watched the match below him.

He added: "I managed to last for the first set but I was feeling really dizzy, even though I was sitting down, and began to sweat a lot. I was convinced I was about to throw up and decided I had better head for the restroom.

"I stood up, took a couple of steps and that's the last I remember until I came round lying flat on my back with a load of people attending me."

Eventual runner-up Murray was in action against Joao Sousa on the nearby Margaret Court Arena at the time, while wife Kim, at the time heavily pregnant, and mother-in-law Leonore watched at their home in Surrey.

"I'm just really sorry I worried a lot of people unnecessarily," Sears said. "But the doctors have assured me my heart is absolutely fine.

"Frankly, I feel a bit of a fraud, but at the time I didn't have a clue what was happening to me and fully appreciate just how terrible it must have looked for everyone watching.

"Quite honestly my timing could not have been worse, with Kim being just a few days away from giving birth. It was the worst possible time in the worst possible place, being so far away from home.

"One thing I am really grateful for is that nothing about my collapse got through to Andy, and the first he knew anything was wrong was when he walked off court and his mum, Judy, told him what had happened.

"He was great. He came straight to the hospital in the tennis clothes he'd been wearing during his match and stayed with me for a long time."

Doctors in both Australia and England are not entirely sure what caused the collapse, but they are certain his heart is fine. Sears, who has since returned to work with Ivanovic, is convinced it was his regular lunch diet in Melbourne.

"I had sushi for lunch 10 days in a row," he said. "I suppose the law of averages dictates that you get one dodgy bit of raw fish in that time."