This syndrome was responsible for the untimely death of Northern Ireland schoolboy Benjamin Robinson in 2011, after he received multiple heavy blows during a rugby game.

Proposals for a three-minute stoppage in football are being considered following a string of controversies in the sport.

Tottenham were criticised last season for letting keeper Hugo Lloris continue playing after he had briefly lost consciousness in a goalless draw against Everton.

During the World Cup in the summer, Alvaro Pereira of Uruguay was left unconscious following a collision with England's Raheem Sterling, but was able to carry on playing after remonstrating with doctors.

The most accurate methods presently available for diagnosing concussion are time-consuming and involve brain scans.

Prof Belli and Dr Grey are keen to offer more options - both for longer-term decisions about a player's recovery, and eventually perhaps for pitch-side diagnosis.

"[Brain scans] are well and good for professional players. But what do we do for the rest of the country? What do we do for the academies and the schools, that don't have access to MRI scanners?" said Prof Belli.

"We just don't have enough MRI scanners in the country, for a start."

They are researching multiple possibilities, including blood tests for chemicals and biological molecules that are released when the brain gets injured, and a new test based on the brain's communication with the muscles.

This second proposal involves using a large magnet to activate small areas of the brain (called transcranial magnetic stimulation, or TMS) while recording the resulting electrical activity in muscles.

The scientists say all these tests show promise, and are closer to being developed than the breathalyser idea. These techniques could be used for "return to play" decisions following weeks, rather than minutes, on the sideline.

Dr O'Driscoll told the BBC he would warmly welcome any additional methods to objectively assess the health of players' brains.

"I think probably, looking at the research that's going on, we're probably not that far off it. It'll take a few years to prove it - it will have to be compared with other tests that we've got," he said.