The 23-year-old has fallen out of contention in Spurs' starting XI in recent weeks due to the form of Mousa Dembele and Clint Dempsey in midfield.
"Obviously he's a player that means a lot to Reading," Villas-Boas told reporters.
"But he's a player that we rate very highly. We brought him here after his amazing contribution (on loan) for Swansea last year and he's a player that we have high expectations for.
"Probably this season at the moment he is not going to the level that he wants, but he's a player that we believe a lot in, and in his future here. We couldn't allow him to leave."
Tottenham face West Brom on Sunday as they look to keep up their challenge for a Champions League berth next season.