England scrum-half Dan Robson has been ruled out for three months with deep vein thrombosis, his club side Wasps said on Thursday.
Robson scored his first international try in England's 57-14 Six Nations win over Italy in March after making his Test debut against France in February. He missed England's final match of the tournament against Scotland through illness.
The scrum-half was first reported to have been suffering from blood clots following the tournament.
"Dan Robson unfortunately developed a deep vein thrombosis," Wasps said in a statement.
"He is currently undergoing treatment which is expected to conclude following three months, after which he will be available to return to full training. This means that he will not be available for selection for Wasps for the remainder of the season, however, should enable him to be available for selection for the World Cup preparations."
England will play four World Cup warm up fixtures before they travel to Japan. They face Wales on Aug. 11 in their first game at Twickenham and complete their warm up series against Italy in Newcastle on Sept. 6.