Klitschko, the WBO, WBA and IBF heavyweight champion has failed to recover in time for the bout in Dusseldorf after undergoing an operation at the weekend to remove a kidney stone.
The Ukrainian, 35, initially hoped he would have recovered in time but has now been advised to pull out.
Berndt Boente, Klitschko's promoter, told a press conference in Dusseldorf: "Wladimir is very disappointed about this cancellation.
"Wladimir is crushed and ruined as he did everything he could to give a show to his loyal, beloved fans. But the pain is too much to overcome at this moment. We have no other choice but to cancel the event."
Boente said there were provisional plans to stage the fight on March 3 as that is the nominal date for Klitschko to fight a mandatory challenger under IBF rules.
"We hope to know in two or three days. Mormeck is also ready to accept it," added Boente.
After undergoing the operation on Saturday Klitschko had to spend the whole day in hospital with a high temperature and inflammation.
"Wladimir shouldn't fight any time soon," German urologist Peter Albertz added during the press conference.
"Anyone who sustains two surgeries in a span of less than 24 hours needs considerable time to rest.
"He is very weak after two surgeries and it makes no sense to have a fight now."
Klitschko's last fight was the heavyweight unification bout against David Haye in Hamburg on July 2 this year where he won a unanimous points victory.
It meant Klitschko added the WBA Super World heavyweight title to his IBF, WBO and International Boxing Organisation heavyweight titles.
The bout against Mormeck would have been the Ukrainian's 20th world title fight in a career of 56 wins, 49 knockouts and only three defeats.
Frenchman Mormeck has had just three fights since he lost his world cruiserweight titles to Haye in November 2007.