CPN-Maoist Chairman Mohan Vaidya said that there could also be collaboration with the former king, "who carries true feelings of nationalism".
66-year-old Gyanendra's reign ended in 2008 when the Constituent Assembly declared Nepal a republic and abolished the monarchy.
At a function in Nuwakot district, Vaidya also said that there was no alternative to the formation of a greater front with all the nationalist forces including the former king on this issue.
CPN-Maoist is leading a 33-party alliance which is opposing the interim election government's plan to conduct Constituent Assembly polls on November 19.
He, however, did not elaborate how and from which side nationalism faces threat.
Claiming that the upcoming elections will not solve Nepal's problems, the dissenting fringe parties have said that it would rather invite a bigger national crisis as the polls were announced by "an unconstitutional government" without ensuring consensus among political parties.
The parties have been demanding that the current Khil Raj Regmi-led dispensation be replaced with a political party-led government and the election scheduled for November 19 be deferred.
The government recently sent an invitation to Vaidya and his alliance for talks in an attempt to convince the protesting parties to participate in the upcoming polls.
