"There is a chance that new party will be formed when people continue to be harassed," he said as he evaded giving a clear answer at a gathering in the north central province.
Rajapaksa allies from fringe parties have been asking the former strongman to break away from Sirisena to challenge him and contest the forthcoming local council elections under a new banner.
The former president, whose nearly a decade-long rule was ended by Sirisena in 2015, has not shown any overly keenness for the move. He has never left Sri Lanka Freedom Party (SLFP) even during its most turbulent times in the 1980s.
A smaller section of the SLFP in the alliance have formed the unity government with Prime Minister Ranil Wickremesinghe's United National Party (UNP).
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Rajapaksa said when his allies are being harassed, they will have no option but to form a new political party.
Sirisena has replaced some of the Rajapaksa loyalists in the SLFP as electoral organisers.
Some of Rajapaksa's key men have faced corruption allegations and continue to be quizzed by the police for alleged wrongdoings during the Rajapaksa regime. His two sons and one brother have spent time in remand over financial misconduct.
Sirisena had broken away from the Rajapaksa cabinet's health ministry job to align with the opposition to be its common candidate.