Leeds Rhinos have signed Cronulla forward Matt Prior on a two-year deal, while captain Trent Merrin has returned to Australia on compassionate grounds.
Prior, 32, made more than 250 appearances in the NRL and represented New South Wales in the State of Origin series.
Fellow forward Merrin, 30, was one year into a four-year deal at Headingley.
"We fully understand Trent's reasons for returning home," director of rugby Kevin Sinfield said.
"He leaves with our best wishes for him and [wife] Jess and their new family."
Merrin made 27 Super League appearances for the Rhinos, scoring four tries.