Candidates are already plotting to run for city comptroller next year — assuming that incumbent Scott Stringer will give up the post to challenge Mayor de Blasio, The Post has learned.

Brooklyn state Sen. Kevin Parker said he’s considering the citywide run because he thinks there’s “at least a 50-50 chance” that Stringer — whom he describes as a “good friend” — will take on the mayor in 2017.

East Harlem state Assemblyman Robert Rodriguez also is considering running for comptroller, sources said.

The jockeying comes as de Blasio faces several federal and state fund-raising probes and his approval rating has fallen to its lowest since his election.