San Francisco police are investigating an incident which left as young Irish GAA footballer in a coma after an incident at a game.
The police were called after Mark McGovern lay prone after an goalmouth incident in the game between San Francisco Celts and the Ulster Club at the GAA grounds on Treasure Island.
The Fermanagh clubman is "critical but stable" in hospital.
The Ulster San Franciso manager Joe Duffy said his club has identified the opposition player involved in the incident .
"As the ball left the goalmouth area the umpires drew to our attention that Mark was on the ground," added Duffy.
"Mark was unconscious and it was obvious it was a serious injury.
"We contacted the San Francisco Police Department and filed a report," added Duffy.
He was rushed to San Francisco General hospital with a serious head injury. Mark McGovern has yet to regain consciousness after a tussle with an opponent on his debut for the Ulster club last Saturday night.
The 22-year-old rising star with the Fermanagh county team remains critically ill after the incident at the weekend.
His parents Danny and Josie and girlfriend Jessica are by his bedside with family and friends and doctors believe he has responded to their presence despite still being unconscious.
Fermanagh GAA spokeswoman Deirdre Donnelly told the BBC that McGovern was showing signs of improvement.
“It is unclear what exactly happened during the off-the-ball incident but he has taken a very serious blow to the head,” said Donnelly.
“We cant jump to conclusions. We don’t know what happened out there. The GAA authorities in San Francisco will investigate the incident and find out what happened.
“We have to wait now to see how Mark pulls through and it will take time to see if there are any long term problems but hopefully Mark will make a full recovery.”
Mother Josie and father Danny have been joined at Mark’s bedside by sisters Connie, Helen and Grace, his uncle Bernard and girlfriend Jessica.
McGovern had travelled to America on a J1 visa to play football for the summer with friends Emmet Scollan and Ciaran Flaherty from his native Belcoo O’Rahilly’s team in Fermanagh.
The three had arrived just a week before their debut for the Ulster GAA club in San Francisco on Saturday night.
“This is worse than a bad nightmare, we are all praying for Mark,” said Scollan.
“Mark’s condition is critical but stable. Doctors have told us that they are pleased and hopeful that he will recover.”
The Ulster Club in San Francisco has also issued a statement. It reads: “We are hoping and praying that Mark will come out of the coma as soon as possible and make a full recovery.
“Mark is being greatly supported by fellow players and his closest friends. Please pray for Mark at this time.”
McGovern had played for the Fermanagh county team in the Dr McKenna Cup competition last winter and is seen as a star of the future by his club Belcoo O’Rahillys.
Club secretary Dominic Kerrigan said: “Mark is an exceptionally talented footballer and one of our most decorated young players who during the past few years has picked up a host of underage winners’ medals.
“The entire community is very saddened and concerned and praying for his recovery.”