City, although impressive in thrashing Manchester United last month and being three points off the top, have already lost twice in their fledgling campaign.
They now face two trips to London, either side of a Champions League journey to CSKA Moscow, and Garcia insists there is no room for error.
The Spaniard told the club's website: "We all know that if we want to be on top at the end of the season we cannot drop any more points.
"Now we have two difficult games away at West Ham and Chelsea.
"There is no other option other than to win all six points. We have already dropped enough points and we are determined to win both games."