Villas-Boas, who has been unable to piece together a winning run of more than three league games this season, has taken fewer than half of the available points from the club's last five matches since beating Roberto Mancini's then-unbeaten Citizens.
"What other teams see is our inconsistency," he said. "That's a fact and what we are trying to put right because we have not been playing to our levels.
"This has been our cancer this season. We are up and down, not in terms of performances sometimes, especially in the December fixtures, but particularly in terms of results.
"So this is the time for action, not words, in terms of our results. The problem is you have to show it on the pitch. At the moment, we have exhausted ourselves in words."
Meanwhile, Chelsea welcome Martin O'Neill's Sunderland to Stamford Bridge this weekend.