The Scarlets have confirmed the extent of back-row forward Barclay’s injury after he was hurt during their Guinness Pro14 semi-final victory over Glasgow four days ago.
Barclay, who will join Edinburgh this summer following a five-year stint in Wales, has undergone surgery and will miss Saturday’s final against Leinster in Dublin.
No time-frame has been put on the 31-year-old’s recovery period, but six months is a normal rehabilitation spell for such an injury.
Scotland face Wales in Cardiff on 3 November, followed by Murrayfield appointments with Fiji, South Africa and Argentina.
Barclay has won 71 caps and was an influential performer when Scotland claimed victories over Australia and England earlier this season.
It had previously been announced that he is among several senior Scotland players rested for the tour of Canada, United States and Argentina next month.
In a statement, the Scarlets said: “John Barclay ruptured his Achilles tendon in the Guinness Pro14 semi final, against (his) former club Glasgow Warriors, on Friday night at Scotstoun Stadium, with the injury requiring surgical repair.
“Barclay underwent surgery yesterday, Monday 21 May.
“Together with the Scottish Rugby Union and Edinburgh Rugby, we have made arrangements for John to begin his recovery and rehabilitation in Edinburgh.”