Modric has been linked with a move out of White Hart Lane all summer, with Real Madrid keen on the Croatia international.
However, nothing concrete has emerged yet, with Spurs demanding £40million for the 26-year-old.
And Villas-Boas has continued to maintain the club’s stance over the transfer fee.
“He (Modric) is training alone because we decided to do that until his mental state is ready to return to the team,” explained the Portuguese.
“It is important that, in the coming days, he understands he must return to the first team.
“We respect the player’s ambition, but he must also respect the club.
“Until we receive a suitable offer for the player, he will not go.
“The contacts we have had with other clubs have not met with what Tottenham wants for the player.
“We respect the size of Madrid and the other interested clubs, but they must respect what we are doing too.”
Tottenham will begin their 2012/13 Premier League campaign with an away game against Newcastle United on Saturday, 18th August.