Simmons, played 13 matches for the Reds this year, one of those at blindside flanker after being released by Queensland as coach Nick Stiles looked to the future.
He and fellow World Cup lock Kane Douglas were both out of favour at the Reds, with Simmons left out of the 23 as early as March when the side played the Jaguares.
Simmons played in 11 of the Wallabies' 15 Tests last year, starting in three of the Spring Tour Tests after an injury to Adam Coleman.