Penrith star Michael Jennings admits he came back a week too early after re-injuring his hamstring in Sunday's embarrassing 42-8 NRL loss to Newcastle.

The NSW Origin centre wasn't originally named in coach Matt Elliott's side but was rushed in at the last minute at the expense of David Simmons.

Jennings said he was never 100 per cent fit and after twinging his hamstring late in the match admitted he was now in major doubt for Friday night's showdown with Parramatta.

The 22-year-old revealed during the pre-season how much he despised the Eels as the Panthers' local rivals, and as he iced up his right hamstring after Sunday's match, declared he would do everything he could to play.

But as he cast a lonely figure as the last man in the Penrith sheds, Jennings regretted the early return and conceded he faced an uphill battle to be fit for Friday night.

"I think I came back maybe one week too early," Jennings told AAP.

"The hammy, I strained it again ... who knows now, who knows.

"It was real late in the second half that I felt it but I guess I've just got to get through it.

"I felt alright but I wasn't 100 per cent. I wasn't confident to let myself go and really test my hammy, I just wanted to test it out and see what I can go with."

Jennings was given until game-day to get right, and on Saturday thought he was good to go.

"It's just all about looking after it now and getting it right for Friday night against Parramatta," he said.

"It's always a good match up against them (Eels) I love playing those games and I don't want to miss this game.

"It'll just be rehab all week, ice, stretching, just all the little stuff that's going to get me right on Friday."

Jennings was scathing about Penrith's performance against the Knights.

"Our completion rate was dog shit ... that was probably the worst game I've been a part of," Jennings said.

Brought to you by AAP © 2024 AAP