Celtic striker Leigh Griffiths has been left out of Scotland's squad for the upcoming friendlies against Italy and France.
Manager Gordon Strachan omitted players from Celtic and Aberdeen, including Scottish Premiership top-scorer Griffiths, so they can be rested ahead of key European ties for their club sides at the start of next season.
Scotland, who failed to qualify for this summer's European Championships, face Italy in Malta on June 29 and France at the Stade Saint-Symphorien in Metz a week later.
"They've had a terrific season," Strachan is quoted as saying by BBC Sport when asked about the inclusion of McKay and Wallace. "As a partnership they work brilliantly together. It's as good a partnership as I've seen for a long time.
"I'm the Scotland manager. My job is to get the best for Scottish football. I'm trying to give [certain players] as much rest as I can so they can be ready for their European ties. It might be a bit of a gamble as I could have done with some of them."
Celtic defender Charlie Mulgrew has been included, but his Parkhead contract is due to expire at the end of the season.
Scotland squad in full:
Goalkeepers: Scott Bain (Dundee), David Marshall (Cardiff), Allan McGregor (Hull)
Defenders: Christophe Berra (Ipswich), Gordon Greer (Brighton), Grant Hanley (Blackburn), Alan Hutton (Aston Villa), Russell Martin (Norwich), Charlie Mulgrew (Celtic), Callum Paterson (Hearts) Andrew Robertson (Hull), Lee Wallace (Rangers)
Midfielders: Ikechi Anya (Watford), Barry Bannan (Sheffield Wednesday), Oliver Burke (Nottingham Forest), Darren Fletcher (West Brom), Shaun Maloney (Hull), James McArthur (Crystal Palace), John McGinn (Hibernian), Barry McKay (Rangers), Matt Phillips (QPR), Matt Ritchie (Brighton), Robert Snodgrass (Hull)
Forwards: Steven Fletcher (Marseille), Chris Martin (Derby), Ross McCormack (Fulham), Steven Naismith (Norwich)