Rangers captain Lee Wallace is among three players to have pulled out of the Scotland squad.
Derby striker Chris Martin and Aston Villa right-back Alan Hutton have also withdrawn from the friendlies against Italy and France.
The Scottish Football Association announced the withdrawals on Twitter but gave no other details of why the players are out.
Wallace, who reportedly has a slight injury, played in Rangers' Scottish Cup defeat by Hibernian on Saturday.
Ibrox manager Mark Warburton had hinted he would withdraw Wallace and Barrie McKay if Rangers won the final and qualified for Europe.
Goalkeepers Allan McGregor and Scott Bain pulled out with back injuries last week, while Hull players Andy Robertson, Robert Snodgrass and Shaun Maloney, plus Sheffield Wednesday midfielder Barry Bannan, are unavailable for the Italy game in Malta on May 29 as they play in the Sky Bet Championship play-off final the previous day.
Swansea left-back Stephen Kingsley, Derby midfielder Craig Bryson and goalkeepers Scott Fox and Jack Hamilton were called up last week.