Thomas Howard, 25, from Durham and team-mate Thomas Baty, 26, died after visiting a nightclub in Colombo during a rugby tour.

Post-mortem tests on Mr Howard found no injury or natural causes for his death.

Further tests have been ordered but police confirmed to the BBC they were looking at whether drugs played a part.

Image copyrightDCRFCImage captionThomas Baty (left) and Thomas Howard complained of breathing difficulties on Sunday after going to a nightclub

The BBC has also seen a preliminary report into Mr Howard’s post-mortem examination, which states the cause of his death needs further investigation.

Tissue, blood and other samples have been sent for analysis, it confirms.

Sri Lankan health minister Rajitha Senarathane said the chief judicial medical officer “couldn’t find the correct diagnosis for the cause of the death”.

“From the post-mortem they can’t find anything so they have taken certain organs of the body and they have sent it to the government analysts,” he said.

• Second rugby player dies in Sri Lanka

• British rugby player dies in Sri Lanka

Asked what might have cause their deaths, he said: “They have played rugger, so they would be exhausted enough.

“After that, they were without sleep until early morning in a night club.”

The men had been touring the country with Durham-based Clems Pirates RFC and begun with a game against Ceylonese Rugby and Football Club (CRFC) in Colombo.

Former Sri Lanka and CRFC player Pavithra Fernando, who was supposed to play in the match but had had a cold, said there had been “no issues” during the game.

“After the match all of us had a friendly drink together in the club and they left around 11pm,” he said.

Sri Lankan police said some British players went to Colombo’s Cleopatra nightclub after the match and returned to their hotel in the early hours of Sunday.

Mr Howard and Mr Baty complained of breathing difficulties to the hotel management and were taken to Nawaloka Hospital, where they died.