Cahill has become Villas-Boas' first recruit of the January transfer window, with the 26-year-old England defender's move from the Reebok Stadium to Stamford Bridge finally being confirmed on Monday.
The Portuguese coach has embarked upon a mission to renovate an ageing Blues side since being appointed as their manager in the summer and it is something Coyle believes Cahill will prove to be a "huge part" of.
"I think there is - as with any player - room for expansion and improvement," Coyle said. "He has now gone to an elite club who have aspirations of winning every competition they enter.
"I think that will push him on to another level, and he is competing with world-class players now for his position in the team.
"He is working with a fantastic manager, who I know well and is someone who wants to build a club at Chelsea. I think Gary will be a huge part of that."
Bolton - who have had a thoroughly disappointing campaign so far and are currently 19th in the Premier League - begin the post-Cahill era with Tuesday's FA Cup third round replay at home against Macclesfield.
Key to Wanderers' lowly standing in the table is their record at their own ground, which shows eight defeats from 10 matches in the league, a far cry from last term when they were only beaten four times there all season.
The Trotters are in a fight for their lives but Coyle feels his side have been gathering some momentum in recent weeks, taking encouragement from their last few performances, which have included a 1-1 home draw with Wolves, a 2-1 victory at Everton and a 3-0 defeat at Manchester United which he thought "flattered" the hosts.
There was also the 2-2 draw with the Silkmen which set up Tuesday's contest and with two more home games - the league visits of Liverpool and Arsenal - to come straight after, Coyle sees it as vital that his team do not take their foot off the pedal against the npower League Two outfit.
"Winning games breeds confidence, regardless of whether it is in the cup or league," Coyle said. "I think our form has been decent recently, and we have to look to carry that on.
"We are getting into a run of games at home and we have to make sure that we are ready to do ourselves justice.
"We know that is the area we have to address. We have to make sure that at home, we are ready, as we were last year when the Reebok was a fortress.
"It can be again, but it only will be with all of us pulling in the right direction and making sure we perform at our highest level."