Newcastle winger Matt Ritchie has withdrawn from the Scotland squad with a knee injury, the club have announced.
Ritchie was included in Alex McLeish's 24-man squad, which he named on Monday. The 28-year-old will miss the friendlies against Peru on May 29 and Mexico on June 2 after suffering an injury in the final day of the Premier League season.
A statement from Newcastle said: "He is now receiving treatment back in Newcastle with the club's medical staff."
Hearts defender John Souttar is also a doubt for the trip to Central and South America.
The 21-year-old received his first senior call-up last week but missed the Jambos' two final Ladbrokes Premiership games of the campaign with a hamstring injury and Tynecastle boss Craig Levein admits he may end up disappointed.
"I'm pleased to see John in the Scotland squad - I just don't know if he's going to be fit and available," Levein told the Edinburgh Evening News.
"He's got that knock so we'll just have to see how he is. If he's 100 per cent then he'll go. We obviously have to make sure he isn't in any danger of making his injury worse. We'll see how he progresses over the next few days."
McLeish named seven uncapped players for these friendlies which included Souttar, Celtic's Lewis Morgan and Hibernian left-back Lewis Stevenson.
The other four uncapped players are goalkeepers Jordan Archer of Millwall and Jon McLaughlin of Hearts, and midfielders Graeme Shinnie of Aberdeen and Hibernian's Dylan McGeouch.