The London club, who lifted the Premier League crown in 2010 under Villas-Boas’s predecessor Carlo Ancelotti, have slumped to fifth in the table after winning just two of their last 10 matches.
Chelsea also have their work cut out to reach the quarter-finals of the Champions League after losing 3-1 to Napoli in the first leg in Italy on Tuesday.
“There is one ... person who takes responsibility — myself,’ Villas-Boas told reporters ahead of Saturday’s home league game against Bolton Wanderers. “The players don’t have to take it and they shouldn’t take it.
“They are top players and they know what they can do for the benefit of the team but there is only one person that is responsible which is me.”
However, Villas-Boas said the loss of captain John Terry for the last five matches had been a big blow.
The former England skipper had knee surgery on Wednesday and the manager expects his central defender to be out for another five or six weeks.
“He is a player we badly miss and is of massive importance to us,” said Villas-Boas, who took over when Ancelotti was sacked by ruthless billionaire owner Roman Abramovich at the end of last season.
“He is a leader and had great performances for us this season ... he was amazing.”
Utility defender Branislav Ivanovic agreed the team were missing Terry’s leadership qualities.
“John is one of the most important players in our team,” the Serb told the club’s website (www.chelseafc.com). “He can change things and do everything positive for the team.
“One of JT’s biggest qualities is his leadership when times are difficult.”
Ivanovic, who joined Chelsea from Lokomotiv Moscow in January 2008, said it was important for all the players to start pulling together.
“This is the hardest moment since I’ve been at the club,” he added. “Confidence isn’t the best but all we can do is try to keep doing things positively and get through this difficult period.
“When we were doing things right it was because the whole team defended well or the whole team attacked well. If we start thinking the defenders are (only) there to defend and the attackers are (only) there to attack, it won’t bring us good results.”
Villas-Boas shrugged off the constant media speculation over his Stamford Bridge future.
“It doesn’t affect me at all,” said the Portuguese. “It is the same whenever results don’t go your way.
“The big lesson might be that in that moment of adversity you have to be aware of extra motivation, extra work to avoid going into a bad run of results that can compromise your position.”
Chelsea will be without injured defender Jose Bosingwa on Saturday while striker Fernando Torres is a doubt after missing training on Thursday due to illness.
Gary Cahill, signed from Bolton last month, is likely to partner David Luiz in the middle of the back four. — Reuters