Paul Lambert's men suffered their first top-flight defeat of the campaign against Arsenal last weekend after a virus had swept through the club's training ground.
Westwood, Nathan Baker and Darren Bent all missed out on the 3-0 defeat at Villa Park as a result, while Andreas Weimann was able to play despite feeling unwell.
Three goals in quick succession after the half-hour mark stunned Villa and there was no way back as they were brought back down to earth.
Lambert's men face another stern test this weekend, but they beat Chelsea 1-0 the last time the two sides met courtesy of Fabian Delph's late goal in a dramatic game that also saw Brazil duo Willian and Ramires sent off.
And midfielder Westwood feels Villa can again cause more problems for the London club this weekend.
"Last year we went there in the middle of a tough run of games, we played them in midweek and we thought we should have got something out of the game," he told the Birmingham Mail, referring to a 2-1 defeat in west London.
"We were unlucky then, but we’ll go there this year with confidence again, just as we did [in the 1-0 win] against Liverpool at Anfield.
"If we play like we did last year at Stamford Bridge, going there and unsettling them and taking them away from their game, then we can hit them with Gabby [Agbonlahor] and the other quick players we have up front."
While Villa had a midweek to recover, Chelsea were given a thorough workout as they beat Bolton Wanderers 2-1 in the third round of the League Cup.
Oscar's second-half wrapped up victory over the Championship sides, which came after draws against Schalke in the UEFA Champions League and Manchester City.
Jose Mourinho's side and Arsenal are the only sides yet to suffer defeat in the Premier League this term, but defender Gary Cahill warned his team-mates not to expect an easy ride against his former club.
"I had a great time at Villa. I owe a lot to them, they brought me through and I had a great time, so I'm looking forward to it," the former Villa man told Chelsea's official website.
"They’ve had a great start to the season, apart from their last result, so it’s going to be another tough test for us.
"At the moment we're unbeaten, we're going well and we should have confidence, especially playing in front of our own fans at Stamford Bridge."
Chelsea could welcome back Ramires (groin), while Villa look set to have a host of players back at full fitness after recovering from illness.
However, Lambert confirmed on Thursday that Ron Vlaar is "really struggling" for Saturday's game due to a calf problem, while long-term absentees Christian Benteke (Achilles) and Libor Kozak (leg) remain out of action.
