Alex McLeish has said Scotland will have to perform acts of “giantkilling” against Peru and Mexico after the number of withdrawals from his squad stretched to six. McLeish, who already had a makeshift party for the upcoming friendlies, lost the Celtic midfielder Stuart Armstrong and the Hearts defender John Souttar on Monday due to injury. The Scots travel to face Peru in Lima on 29 May before a meeting in Mexico City on 2 June.

“It is getting quite thin,” Scotland’s manager said of his squad. “We have some great players out there and we want them to be ready and available to play for Scotland. Hopefully we can do a giantkilling act. Wigan beat Manchester City in a recent FA Cup game so we are looking for those kind of performances and the fellows to play above their performance levels like they have never done before.”

McLeish hinted at the late additions of United States-based players to bolster his squad. The former Liverpool defender Danny Wilson now plays for Colorado Rapids while Sam Nicholson, the former Hearts winger, recently moved to the same club from Minnesota United. “There’s a couple of other Scottish boys out there who have good experience we can maybe call upon,” McLeish said. “We will assess things on Tuesday morning.”

The Scotland manager is aware of wider scepticism regarding the motivations of players at the conclusion to their domestic season. McLeish, who has taken charge of only two fixtures in his second Scotland tenure, admitted he must tread carefully with regards to building relationships with clubs. With Scotland not in the World Cup, clubs have no obligation to send players on international duty for friendlies. McLeish earlier opted not to call upon a key batch of Celtic players when mindful both of their need for rest and Champions League qualifiers in mid-summer.

“You have to hope everyone else genuinely wanted to come to play for their country and enhance their careers,” he said. “It is not to be. It is a shame to lose Stuart, a tremendous player. But we are looking forward to the overall grand scheme of things.

“ Sometimes managers can rage and say, ‘Well listen, we are wanting to do a medical with them’ but we have to trust in the clubs and we have to have a rapport with the clubs. That has definitely got to be an ongoing thing.”

He added: “It has been very difficult at this particular time with the end of the season and players playing on with injuries in the last few weeks. We have made some concessions with James McArthur and that kind of thing but the late call-offs were disappointing. But I am not blaming the players.

“Stuart has a little tweak in his hamstring, he flagged it up right after the Scottish Cup final on Saturday.

“John Souttar is gagging to play for the full national team. He has come through the system and the process and had a good season, so hopefully he will keep learning and improve on what has been a very good season for him.”