However, Villas-Boas has held talks with Caulker and is confident that the player will be suitably prepared to play if selected.
"We spoke to the player," said Villas-Boas. "At the moment we don't have enough information, nor do the FA, although there is contact between the FA, the government and the embassy in Serbia to try to find out more information about the speculation that is coming out.
"Regarding the player I think he will be ready to play. I think he obviously has a good chance because he has been doing quite well to make selection.
"I am not worried yet with the consequences of what can happen. We are still finding out more information."
Caulker has made five Premier League appearances this season, scoring one goal.