James McCarthy continued to be assessed on Monday after reporting for international duty with the Republic of Ireland.
The Everton midfielder complained of a tight hamstring following his club’s 1-1 Premier League draw at Sunderland on Sunday.
Glasgow-born McCarthy is manager Martin O’Neill’s biggest doubt ahead of Friday’s Euro 2016 qualifier against Scotland at Celtic Park.
He and full-back Stephen Ward headed for the gym as their team-mates warmed up at Gannon Park in Malahide with midfielder Glenn Whelan among them just weeks after fracturing a bone in his leg during last month’s draw in Germany.