The German midfielder has agreed to join Spurs on a free transfer at the end of the season when his current contract with Schalke runs out.
However, Villas-Boas wants to recruit the 22-year-old this month because of recent injury problems to his midfielders.
"At the moment, it's very, very difficult, but let's see," ESPNSoccernet quotes the Portuguese as saying when asked about Holtby's early arrival.
"At the moment, there is nothing [lined up about signing other players]. It's very difficult. The only thing we have done at the moment is hold onto the midfielders that are here."
Tottenham are currently fourth in the Premier League table.