Webster scored 15 tries in the Robins' promotion-winning season
Hull KR have released scrum-half James Webster, paving the way for fellow Australian Michael Dobson to complete his move from Canberra Raiders.
Webster, 28, whose season was ended by a shoulder injury, was one of Rovers' three permitted overseas players.
Dobson is expected to sign next week after agreeing a move on Wednesday.
Chairman Neil Hudgell said: "It is extremely disappointing that we have to announce his departure in such unfortunate circumstances."
Robins coach Justin Morgan told BBC Radio Humberside: "James has been fantastic for the club and we need to thank him."
Webster signed for Rovers in 2005 and played 98 games as they won promotion in 2006 and retained their Super League status last year.
James has been a leading light in the improving fortunes of this club, he came to the club at the most challenging of times
Hull KR chairman Neil Hudgell
Hudgell added: "James has been a leading light in the improving fortunes of this club.
"He came to the club at the most challenging of times and has built up a great reputation in and around the city. Not only has he been a front-line performer on the field, he has been a fantastic ambassador for the club off it."