Hiddink’s stay as Chelsea boss will end at the weekend.
The Dutchman said: “The people at this club know they must improve in depth.
“We have a good squad and a good team, but everyone knows that Chelsea has to compete in three competitions.
“You need a squad not just of 14 or 15 or 16 players, but you need quality players all over the place.
“But that’s not up to me, that will be up to the new manager and the board, of course.”