Doctors even prescribed medication for meningitis as a precaution as they looked for a cause before eventually attributing his symptoms to a bug.

Walters said: “I had woken up in Dubai and started to get headaches and my eyes got worse. By the time I landed, I was struggling to drive home from the airport. I got a good night’s sleep, but the next morning I woke up the same, just really, really bad headaches.

“My eyes were really sore and I couldn’t look up at the light. I was struggling all day and went to hospital that night.

“Because I had headaches and the like, they put me straight through and put me on a drip and gave me antibiotics for meningitis just in case.

“They have to take it as a worst case scenario, so they gave me that on a drip and then a few hours later, I had a blood test. Then at 1am, they said it had all come back clean and it could be a migraine.

“But that evening, my daughter had the same thing, headaches and she was throwing up all night, so it must have been a bug. But they don’t know - all the blood tests came back clean.”

Walters’ condition – and that of his daughter – improved so rapidly that he had a flight booked to America for the say after he was released from hospital.

However, Ireland doctor Alan Byrne advised him to remain at home for a couple more days, and he arrived in Philadelphia on Friday just in time to board the team coach for the friendly clash with Costa Rica.

He said: “I was trying to get over but Alan, the doctor, said to stay away for a couple of days and see how your daughter is first, make sure everything is okay.

“I was desperate to get over really. I came over on Friday, which was a long day. I just made the bus to get to the Costa Rica game.”

Walters warmed up with his team-mates at PPL Park, but did not play any part in the game, and he is keen to get his chance against another of the World Cup finalists, Portugal, in New Jersey during the early hours of Wednesday morning.

He said: “I would like to be involved – hopefully I will be. There are a lot of lads who want to play, so we will see what team he [manager Martin O’Neill] picks. But I’d like to be involved.

“It’s their [Portugal’s] last game before the World Cup starts, so depending on who plays, I’m sure there will be players who will want to impress.

“It’s a great. They are the games you want to be involved in.”

Walters endured a frustrating end to a good season for club Stoke when a red card and subsequent three-match ban cost him his place in the team.

He was dismissed for a high challenge on Norwich’s Alex Tettey on March 8 and two months on, still feels the decision – or at least the punishment – was harsh.

The frontman said: “I took a bad touch off my chest and it bounced. We have both gone for it and he’s literally just nicked it before me.

“Yeah, it was harsh, like as if I head-butted him. I got sent off for violent conduct – that’s what I got marked down for.

“I think the scream got me sent off. I went in to see the referee after and he just said he had to put it down as violent conduct.”