The 29-year old has reportedly been offered a four-year contract by the English Super League club from the 2019 campaign, but would first require an early release from Penrith, where he is contracted for two more seasons.
The former Kangaroo has played seven tests for Australia as well as 13 games for the NSW Blues, with his last State of Origin appearance coming in 2015.
Merrin would become incoming Leeds coach David Furner first boom recruit, who is looking to instantly upgrade his team.
Leeds struggled this season and looked like getting relegated at times, finishing with eight wins.
The Panthers have re-signed several key players ahead of the 2019 season, including Nathan Cleary, Regan Campbell-Gillard and Viliame Kikau, while only losing Christian Crichton and Corey Harawira-Naera to the Bulldogs and probably Tyrone Peachey to the Titans.