The Blues failed to close the gap on leaders Arsenal as they were stunned by the Potters at the Britannia Stadium.
"There is no other way than working hard," he told the club's official website. "Playing well is not enough.
"We have to score more goals and we have to stop the individual mistakes at the back because mistakes cost us goals and points."
Chelsea finish their successful group campaign in the Champions League on Wednesday when they play host to Steaua Bucuresti.