The 33-year-old Aston Villa man is yet to play for his club this season because of a persistent groin problem, but was put on stand-by for Wednesday night's friendly with Poland at the Aviva Stadium when Trapattoni named his latest squad last month.
Trapattoni said: "I spoke with him and I said 'okay. He wants to come back, he wants to be here', but I said to him that at this moment, I don't want to make trouble with the club.
"We need him for the matches and it will be important that he gets through these medical tests.
"I hope he can be ready for the matches."