Parramatta have been rocked ahead of their semi-final against South Sydney after Michael Jennings was stood down for testing positive to performance-enhancing substances.

Jennings was on Saturday morning provisionally suspended by the NRL, after returning a positive test on September 21.

It leaves the veteran Eel and former NSW and Kangaroos centre’s career in jeopardy as he tries to clear his name at the age of 32.