Modric has been training separately as he waits to resolve his future, having made it clear to Spurs that he would like to leave this summer.
Real Madrid have been linked with a swoop for the Croatian but still nothing has been finalised, several weeks after Villas-Boas admitted talks had been held with several clubs about a move.
Chairman Daniel Levy is not prepared to sell such an important player on the cheap and Villas-Boas believes Modric must accept that Tottenham are not to blame.
The head coach says he can then start to work with the rest of the group as normal, but it looks doubtful that he will be ready for the start of the season.
“He has been training separately. Now it is important for Luka to feel mentally ready to come back to first-team training,” Villas-Boas told Sky Sports News after Sunday’s 1-0 friendly victory over Watford, which Modric missed.
“These boys are at a different level in terms of their preparation, concentration and commitment.
“I think the player has to understand that the club cannot do anything about other clubs’ offers.
“We have a value and an interest that we have to defend, and we are waiting to reintegrate the player if the offer is not matched.”
It was a similar tale for Modric last summer when he had set his heart on a move away from the club but ended up staying and playing an important part in Tottenham’s season.
Villas-Boas has no doubt that he would again get his head down and commit to Spurs if there is no move during the current transfer window, but he admits the uncertainty is not ideal.
“We will try to solve it as soon as possible,” he said. “It is the second time we have been through this situation.
“It is obviously difficult for him, but the chairman is defending the club’s interests and the player has to understand that, and the fact that the offer does not meet the chairman’s demands means we can’t do anything.
“The player is a good professional and hopefully he will return to the team.”
Asked if Modric could be involved at the start of the season, Villas-Boas added: “Obviously he will have to raise his fitness level, and the sooner that we can have him reintegrated mentally and then physically, we will then see how things go.”