The transport system bringing fans to the stadium for Northern Ireland's game could be overloaded, the president of Lyon's French-Irish Association warned.
Thousands will take to trams, Metro and buses on Thursday afternoon bound for the Stade de Lyon in France for the crucial Ukraine clash. Eoin Campbell urged them to leave lots of time for their journey.
Special arrangements are due to be introduced in one of the country's largest cities three and a half hours before kick off, with shuttle buses to the stadium.
Mr Campbell said: "They are here for the match, they want to see the match, it would just be a real pity if people were heading out and they missed the start of the match - they would be gutted.
"I reckon it is a bit overloaded and that could be a problem.
"I would advise people to get moving."
He said there was an alcohol ban around the stadium, part of a suite of emergency measures taken by the French government to ensure safety.
"Allow plenty of time for the journey."
Mr Campbell, from Warrenpoint in Co Down, said the European Rugby Champions Cup final was held in Lyon last month and getting out of town seemed to be an overload on the system. There were huge delays where fans transferred from the Metro onto shuttle buses to the ground.
The Green and White Army has already suffered severe travel disruption, by train across Provence from the opening fixture in Nice and by air from Northern Ireland after French transport workers took industrial action over Government reforms.
A spokeswoman for Lyon transport company TCL said: "We transported 38,000 people Monday for the match between Belgium and Italy.
"Everything went well.
"For Thursday's game, the service by shuttle (bus and tram) is set up from 14:30. The fans should anticipate their path and not go to the stadium at the last moment.
"For the return, shuttles run until 21:30, we advise fans not to rush."
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