Wasps scrum-half Dan Robson says being diagnosed with deep vein thrombosis just five months before the Rugby World Cup was a “freak thing”.
The 27-year-old, who has won two international caps, was ruled out for three months in April and missed out on England’s 31-man squad for Japan.
“Something like that is not just really an injury,” Robson told BBC Sport.
“It is to do with your health as well so it makes you think a lot more. It was very difficult.”
Robson made his England debut during this year’s Six Nations, appearing from the bench in the games against France and Italy – scoring a try in the latter match.
He was then withdrawn from the squad to face Scotland on 16 March after the discovery of blood clots, which Wasps said “arose spontaneously” in the week before the game.
“I had to go through a lot more different stages and make sure my health was the main priority,” Robson, who is now off medication and back in full training, added.
“It was tough, and being in the middle of the Six Nations was not ideal timing.
“I have had all the blood tests done and sat down for hours on end trying to think of what could have made it occur.
“We came to the conclusion that it was one of those freak things – I probably got a knock and had a little bleed.
“It might have been lurking there for a little bit. It was frustrating and I’m glad we found it when we did.”
Robson ‘told to be ready’
England coach Eddie Jones named Robson in a training squad for a camp in London at the end of June, but the Wasps man was not included in the 38-man squad for a training camp in Italy the following month or the final travelling party for the Far East.
“It is a World Cup and I want to be there,” Robson said. “It is not something I have hidden.
“You are always frustrated [at missing out on a squad] as you want to be playing for England.”
Robson has been named co-captain of Wasps for the start of the domestic campaign while regular skipper Joe Launchbury is away on duty with England in Japan.
However, with Leicester’s Ben Youngs and and Gloucester’s Willi Heinz the only scrum-halves in the England squad, Robson could yet be handed a late call-up to the if injury or illness arises.
“That’s all I have been told – to be ready,” he added.
“Things happen and it is a long tournament. The training we are doing at Wasps is definitely going to keep me in shape.”
The English domestic season kicks off on Friday, 20 September, with the Premiership Rugby Cup, followed on Friday, 18 October, with the start of the Gallagher Premiership Rugby campaign.