Mayo forward Cillian O’Connor has suffered a "significant shoulder injury" in action with his club Ballintubber, casting a huge doubt over his participation in the rest of the Championship.
O’Connor will have a scan on his shoulder on Thursday.
A Mayo GAA statement read: "On Saturday 25 May while on club championship duty for Ballintubber, Cillian O'Connor suffered what can be described as quite a significant shoulder injury.
"The injury sustained was to the same shoulder as Cillian previously hurt last October. While the initial diagnosis is that Cillian has suffered a dislocated shoulder to a similar injury suffered last year, more assessment is needed.
"Cillian will undergo a further scan next Thursday and will meet with the specialists then to determine the extent of the injury and the treatment required.
"Cillian will continue to work with the excellent medical team who will no doubt have Cillian back playing for Mayo as soon as he is physically able to.
"In the meantime we wish Cillian all the best in his recovery and look forward to seeing him again very soon in the Green & Red of Mayo."
O’Connor was part of the Mayo side that crushed Galway in their opening match of the Connacht Football Championship this month.
They meet Roscommon in the semi-final.