The Parramatta Eels have confirmed that Will Penisini's late withdrawal from last weekend's surprise win over the Brisbane Broncos came about due to a groin problem.

Penisini, who was replaced by Jordan Samrani for the game, and will be again this weekend, is now expected to miss a month with the injury.

The club have confirmed it was adductor related groin pain that saw him ruled out of the match, and will now cost him the next four weeks, although it's typically a tricky injury to manage, so there is no guarantee on his return.

Penisini, as a result, will miss this Sunday's clash with the St George Illawarra Dragons at home, as well as other matches against the Penrith Panthers, Wests Tigers and Gold Coast Titans in the coming weeks before being a chance to return in Round 7 against the Canterbury Bulldogs in a grudge clash.

Samrani will be up against Brian Kelly to retain the vacant spot in the centres while Penisini is sidelined.

The Eels have also confirmed back-up half Ronald Volkman will miss the next fortnight, having suffered a quad strain. He is yet to make it onto the field at NRL or NSW Cup level this year.