Norwich City have confirmed the 29-year-old has sustained knee ligament damage and won’t return to action until the beginning of next season.
This is a significant blow for manager Steve Clarke, who has used the former Aberdeen star regularly in recent international matches, either from the starting XI or off the bench.
Chelsea youngster Billy Gilmour will be among the favourites to take his place in the squad, while attacking midfielders David Turnbull of Celtic and Farense star Ryan Gauld will also earn consideration.
Norwich announced on Tuesday: "Kenny McLean is set to be out of action for a period of 12 weeks following confirmation of a knee ligament injury.
"The Scottish midfielder was forced from the field of play following a heavy challenge in the 52nd minute of City’s 2-2 Sky Bet Championship draw away at Barnsley.
"Subsequent scans and further assessments have since revealed significant damage to the medial collateral ligament in McLean’s right knee.
"McLean will now undergo further assessment with an orthopaedic consultant to ascertain a management and rehabilitation plan for the injury.
"The injury will rule McLean out of Scotland’s upcoming UEFA European Championship campaign.”
Meanwhile, striker Lyndon Dykes has been cleared of any serious damage after suffering his own knee injury in Queens Park Rangers’ final game of the campaign.
The Australian-born target man netted six times in his last eight games after going through a four-month goal drought earlier in the campaign, though he was forced off at half-time against Luton Town.
Scans have since revealed that there is no significant damage and he’ll be fit when the Scotland squad meet up ahead of this summer’s tournament.
QPR boss Mark Warburton said after the Luton match: “Lyndon picked up a knock but he was keen to play on. The doc said no, and it’s important we protect our players.
“We know he has a big summer ahead with Scotland – I just hope he doesn’t score against England!”