Drogba believes the Blues had under-estimated their Champions League opponents.
The Ivorian striker told Sky Sports Xtra: “We were not concentrating. We thought, maybe, it was going to be an easy game but in the Champions League there are no easy games.
“We said 2-1 was going to be a good result but Apoel gave everything.
“We will go to training and try to correct what went wrong.
“This was frustrating because we had some chances – a lot of chances – but we have to play more together and defend together too.”