The Magpies centre half took the armband for his country early on after Granit Xhaka was replaced after the half hour of their 2-1 friendly defeat to Croatia.
Schär started the game at the St. Gallen Stadium, and saw his side take the lead through Mario Gavranovic’s fine header from Xhaka’s cross.
And when Arsenal midfielder Xhaka went off soon after, Schär took over captaincy duties - but was powerless to prevent Josip Brekalo’s leveller just before the break.
Mario Pasalic’s second half winner completed the turnaround for Croatia, with United’s Schär’s being withdrawn with quarter of an hour remaining and Loris Benito taking his place.
Last weekend, he made his first start of the campaign after recovering from a shoulder injury sustained at the end of last term, helping Steve Bruce’s men beat Burnley 3-1 at St. James’ Park just before linking up with the Switzerland side.
The Rossocrociati now face a UEFA Nations League double-header, as the travel to Madrid to take on Spain on Saturday before a trip to Cologne to play Germany on Tuesday.