Manager Villas-Boas has revealed the 23-year-old World Cup winner, for whom Chelsea reportedly paid Valencia around ?24million, is unlikely to start Saturday's Barclays Premier League game against Norwich, although he could well be on the bench.
"This league is very, very specific in terms of intensity, emotionally and culturally," Villas-Boas said. "It doesn't mean he's not threatening the starting XI, but two training sessions is short for a player creating new relationships with the players. Friday is a decisive day in terms of the strategic part of our game, so that's when we'll decide."
Villas-Boas has repeatedly insisted he is happy at the quality of the squad he inherited from predecessor Carlo Ancelotti, but the arrival of Mata and his pursuit of Luka Modric and Alvaro Pereira suggests otherwise.
He added of Mata: "We were looking for a player that gives us some creativity in the final third. Not that we don't have that, but you always want to add it when you can find talent of this nature.
"The price was reasonable for his qualities and what he's shown in the Spanish and Champions League. He's an addition that everybody was looking forward to.
"He has an eye for goal and a magnificent record for assists throughout his career since joining Valencia from Real Madrid B."
Arsenal failed in a bid to land Mata before Chelsea pounced, and Villas-Boas revealed he too came close to missing out on the Spain star.
"It was difficult in the beginning of the negotiations with Valencia," he said,
"For them, he was one of their biggest assets and they weren't very open to talk. We lost a couple of days in that situation while we were colliding, but that was okay."
Source: PA
Source: PA