Clark was expected to arrive at the Republic's Portmarnock base on Monday evening as the Italian faced up to the loss of central defender Sean St Ledger and midfielder Glenn Whelan, who were both due to have scans on Monday afternoon.
The pair suffered hamstring injuries while playing for Leicester and Stoke respectively over the weekend and are rated as extremely doubtful to be fit for the World Cup qualifiers against Germany and the Faroe Islands.
In addition, Sunderland winger James McClean has been ruled out of the clash with the Germans at the Aviva Stadium on Friday evening after a scan on Wearside revealed the extent of the hip injury he suffered during his club's 3-0 Barclays Premier League defeat at Manchester City on Sunday.
A spokesman for the Football Association of Ireland said: "The results of James McClean's scan this morning in Sunderland showed a grade one hip flexor strain which will certainly rule him out for the Germany match and may exclude him for the Faroe Islands.
"McClean will remain at his club to receive treatment."
Trapattoni, who was already without experienced defender Richard Dunne, lost striker Kevin Doyle on Friday after he picked up a thigh problem training with Wolves at the start of a costly few days for Ireland.