Klitschko says he will only take the December 10 fight in Manchester if the WBA belt is on the line too.
The WBA and WBO belts have been freed up by Tyson Fury who handed them over to concentrate on his battles with depression and drug use.
Joshua's manager Eddie Hearn said the next 48 hours would be vital as they seek a ruling from the WBA. In the meantime he confirmed he is looking at other options.
Hearn's easiest backup route is to call out Parker who is the mandatory challenger with the IBF.