The Blues face Sparta Prague tomorrow night as they look to progress to the Europa League last 16, before attentions quickly turn to Sunday's potentially decisive Premier League trip to the Etihad Stadium.
Just four points separate the reigning European champions in third and the hosts, whose manager Roberto Mancini recently downplayed talk of being beaten to second place.
"I think we've obviously got a huge game tomorrow night, and then a massive game on Sunday," Cahill said.
"If we get a positive result on Sunday then that opens it right back up.
"We're taking it one game at a time but we'll be looking to do that on Sunday.
"It'll be tough game away from home, but if we do get a positive result then obviously second place is within touching distance."
The centre-back was keen to steer talk away from the City game this afternoon, preferring instead to focus on tomorrow's second leg against Sparta Prague.
Oscar's goal in the Czech Republic last week puts Chelsea in the driving seat for the home leg, but Cahill insists there will not be any complacency at Stamford Bridge.
"You've always got to take teams seriously," he said. "They're a quality outfit, and made it tough for us away from home.
"But we got a positive result, the away goal, but we still won't take it lightly. They've got some great players.
"Our home form in Europe is nine unbeaten, so hopefully that can continue."
Frank Lampard and Branislav Ivanovic are both being rested for tomorrow's game, while Demba Ba is cup-tied due to his earlier involvement with Newcastle.
Cahill is expected to start in defence, where he could be joined by John Terry as he continues his return from injury.
The Chelsea captain has started three of the last six matches after missing the festive period with a knee complaint.
"He's a massive character and leader for us," Cahill said. "He's been struggling with his injury a bit, but has come back again.
"It's just great to have everyone back fit. You don't want people sitting in the treatment room if you can help.
"To have most of the lads back out there with us now is a healthy situation."