Duceppe, who has been keeping a low profile since his party was decimated by the NDP in the last federal election, accused Quebec solidaire co-leader Amir Khadir of being shallow and opportunistic.
Khadir, the sole member of Quebec solidaire in the provincial legislature, has come out in favour of Quebec sovereignty but has acknowledged he voted for the NDP in the May 2011 election when the Bloc suffered the worse defeat in its history, prompting Duceppe to step down as the party's leader.
Duceppe said in an interview with The Canadian Press that he didn't respect people who say they're sovereigntists and then turn around and support federal parties.
"I respect the people in Quebec solidaire, like Francoise David," Duceppe said, citing the party's co-leader with Khadir. "I don't respect everyone because some don't deserve it, like Khadir."
His criticism of Khadir arose when he was asked how the PQ would fare with sovereigntist support being split among other pro-independence parties.
Duceppe derided Quebec solidaire's slogan which roughly translates into English as "stand up."
"You can't pretend you're standing up when you're on your knees in front of a federal party," he said, referring to Khadir's NDP support.
He also described Khadir as someone who "has simplistic responses to complex questions."
Duceppe will attend a PQ rally in his riding on Saturday to support Jean-Francois Lisee, the sovereigntist candidate.
Duceppe has mainly stayed out of the election because he's awaiting a decision by a House of Commons committee on whether he improperly paid the Bloc's director general out of public funds.
"I am strongly hoping for a Parti Quebecois victory and I will do what I can to help," he said.
He said he is "available" to play a role in the election but was coy on whether or not the PQ had asked him to be involved.