Chelsea have been rocked by the news that goalkeeper Petr Cech has been ruled out of action for up to four weeks after suffering a knee injury in training.
Cech out for four weeks
Cech fell awkwardly at the end of Wednesday's session and scans later revealed the Czech Republic international had suffered medial ligament damage.
Cech will also miss the following weekend's Premier League match against newly-promoted Norwich, but the international break means the 29-year-old could recover in time to face Sunderland on September 10, with a trip to Manchester United to follow.
Villas-Boas said: "Petr Cech yesterday suffered a medial ligament injury and will be out for three to four weeks. It was the end of training, a normal training incident. He fell awkwardly with his weight on top of him. We expected much worse when we saw the incident.''
Back-up keeper Turnball, who signed from Middlesbrough in 2009, made two starts last season - against MSK Zilina in the Champions League and Newcastle in the Carling Cup - while Hilario was on the bench for Chelsea's Premier League opener against Stoke last weekend.
Teenage goalkeeper Thibaut Courtois joined Atletico Madrid on a season-long loan straight after signing for Chelsea from Genk last month.
Meanwhile, Romelu Lukaku has completed his move from Anderlecht to Chelsea for a fee reported to be around £20 million and the forward will be available for the weekend clash with West Brom at Stamford Bridge.