The 33-year-old, who is heading into the final year of his contract, is currently in talks with the former Premier League champions over a one-year extension.
"We will [reach an agreement],” Villas-Boas told reporters. "He is one of the most important players and representative players of the club.
"And his willingness to continue is 100%. It will be because of that that we will reach an agreement."
Chelsea go head to head with West Bromwich Albion at Stamford Bridge in the late kick-off on Saturday.