Jose Mourinho has drafted in Steve Sidwell, Tal Ben Haim, Claudio Pizarro and Florent Malouda as reinforcements - vital for when the club loses players to the African Nations Cup in January.
Cech told FourFourTwo magazine: "We lost the title last year because of injuries and that comes down to luck. We cannot say that we made a mistake. I think our squad for the season is now complete with the new arrivals.
"Maybe someone else will join us but I'm sure that if we get any injuries we'll be able to handle it."