Swanson comes into the squad after Celtic captain Scott Brown was ruled out with an ankle injury.
There is no place for Hibernian striker Garry O'Connor, who took his goal tally for the season to 10 with a double against St Johnstone on Wednesday night, or his former Easter Road team-mate Steven Fletcher.
Fletcher recently claimed he had not made himself unavailable for selection despite asking not to be considered for the Carling Nations Cup tie with Northern Ireland in February, but his exile continues.
Scotland manager Craig Levein bought Swanson from Berwick while Dundee United manager and has called him the most talented player he has worked with.
The 24-year-old would have been in earlier squads but missed out through injury, but has recovered from early-season fitness problems to net in each of United's last two Clydesdale Bank Premier League games.
Brown is out with the ankle injury he first picked up in Scotland's friendly win over Denmark in August, with Celtic manager Neil Lennon fearing he faces more than a few weeks on the sidelines.
Levein has made three changes in all in his 25-man squad for the games in Vaduz on October 8 and against the world champions in Alicante four days later.
Cardiff goalkeeper David Marshall comes in for Preston's Iain Turner while Middlesbrough defender Stephen McManus returns to the squad. Liverpool centre-back Danny Wilson has dropped out.
Source: PA
Source: PA