Former Porto defender Fernando Nelson believes that Andre Villas-Boas's days are numbered at Chelsea following a number of disappointing results.

Pressure has mounted on the Portuguese manager, with suggestions that the 34-year-old is not meeting expectations at Stamford Bridge.

"I don't think [owner Roman] Abramovich will be patient with him," The Sun quotes Nelson as saying. "Villas-Boas will only be there until Chelsea's next defeat, the match against Newcastle at the weekend or against Valencia in the Champions League.

"This is a critical week for Villas-Boas. He knows it could be his last at Chelsea and is already prepared for that. Abramovich had no patience with Jose and he must regret getting rid of him as it was his biggest mistake at Chelsea.

"Villas-Boas should have stayed at Porto. He had a strong squad, the players were settled and knew what to do. Things happened automatically. If he'd stayed there this season, Porto would have been among the top four clubs in Europe. But Andre has gone to Chelsea too soon."

Despite concerns over the Blues boss's future, Abramovich is reportedly fully behind Villas-Boas to turn the club's fortunes around.