Kiba Richards, who last played for Raiders in 2007, has re-joined the club, and No 8 Mike Stubbs has also signed but Sullivan has left to give things a go at Championship side Esher, who play two divisions above Raiders’ National 2 South.
Winger Richards was with Welsh Premiership side Tonmawr last season, after a couple of years with Ealing.
His signing delighted Raiders chairman David Hinchliffe, who said: “Kiba wants to move back down here and we’re pleased to have him back after he played for us a few seasons ago.
“He’s a winger or outside centre but has a lot of pace and is big, and opposition players won’t enjoy him running at them.”
Stubbs was with Welsh Premiership side Pontypool last season but has moved down to the local area and Hinchliffe said: “Mike’s moved to the area and we’re pleased to have him on board as well.
“We’re also still talking to another couple of players and have another player coming down for a two-week trial this week.”
Hinchliffe has wished Sullivan all the best on his move to Esher and said: “Greg wants to give it a go to see if he can step up and we’re happy with that.
“We’d all be really pleased if he goes up there and does well.
“As a club, we’re all for players moving on to a higher level of rugby.
“But, if things don’t work out, he’ll always be welcomed back. The door will always be open for him.
“He’s a good young player and has the chance to move up two levels.
“He was our players’ player of the year last season and if he makes it, it will be another success story for the club.
“If not, we’d love for him to come back and play for us again.”
New Raiders coach Kieron Dawson will take charge of the club for the first team on August 13 when they host Barking in a pre-season friendly. (2pm)
Their National 2 South league season starts on August 27, when they travel to Clifton.