James Segeyaro will spend at least one month on the sidelines after scans revealed the extent of the knee injury he suffered against the Bulldogs on Saturday.
With about 20 minutes left in the match at ANZ Stadium, the Panthers hooker fell awkwardly and was assisted from the field.
Scans on Monday revealed Segeyaro suffered a grade two medial ligament tear in his left knee, with an expected recovery time of four to six weeks.
The Panthers next play Wests Tigers at Leichhardt Oval on Sunday afternoon before returning home to Pepper Stadium to face the Rabbitohs on Friday, July 3.