PAS president Abdul Hadi Awang said a merger with Umno will not be easy as the latter is sinking.
"Umno is currently a sinking ship. When we go to sea, if we approach a sinking ship, we may also sink with them.
"Merging with a party that has a leak (in its ship) is difficult and cumbersome," he was reported as saying by Harakah Daily today.
Hadi made the remarks at a dialogue in Dublin, Ireland on Sunday.
Despite comparing Umno to a sinking ship, however, the PAS president stressed that it is not easy for any party or ideology to die.
"Some say that Umno is in the grave, but it's not that easy.
"The outlawed Communist Party still has followers. Adolf Hitler's (Nazi) party still has followers. Even the devil has followers.
"I'm not saying they (Umno) are the devil, no, but it's not easy to kill off an ideology, there will be successors," he said.
Umno and PAS became allies following the 14th general election.
However, both parties insist that their cooperation is only on issues pertaining to the Malays and Islam, and have repeatedly ruled out a merger.
Last week, PAS vice-president Mohd Amar Nik Abdullah said that Umno should be dissolved, so that its members can join the Islamist party.