Donegal have reportedly suffered a major blow ahead of their Super 8 game against Kerry at Croke Park on Sunday.
According to Highland Radio, Eoghan Bán Gallagher suffered what is described as a "serious leg injury" in training.
BBC Northern Ireland's Thomas Niblock adds it is a broken ankle which Bán Gallagher has sustained.
The defender has been a key player for Declan Bonner's side this season.
He was nominated for an All-Star last year and was named at corner-back in the Sunday Game Team of the Year. He was also the Donegal Footballer of the Year for 2018.
The Ulster champions won their opening game of this year's Super 8 stage against Meath at the weekend. Mayo, in Castlebar on the August Bank Holiday weekend, will be their final opponents of the All-Ireland quarter-finals.
Photo by Sam Barnes/Sportsfile