Mannix, whose stand-off place in the side for last night's Allied Dunbar Premiership match at Newcastle was taken by his compatriot, Shane Howarth, has been a key figure is Sale's success over the last two years.
He helped them to the Pilkington Cup final last May and was in the side that beat West Hartlepool last month to take them closer to a return to Twickenham.
Sale's chief executive, Howard Thomas, said: "Simon Mannix is a top-class player. Unfortunately, there are certain issues over which he and the rugby management could not agree."
The move is certain to alert a number of leading clubs, with Saracens expected to lead the way. They need a replacement for outside-half Michael Lynagh, who retires at the end of the season.
Mannix said: "It is a shame I'll be leaving because I have enjoyed my time playing rugby in the North-West and my family and I were made to feel very welcome by both the club and its supporters. I wish the club every success in the future."
Wasps' rugby director, Nigel Melville, yesterday challenged one of the most partisan crowds in English rugby to give the England captain, Lawrence Dallaglio, his second rough ride in successive matches.
The Wasps flanker was called "Judas" by a handful of the crowd at Saracens last Sunday and he can expect more of the same from occupants of Kingsholm's Shed tonight, when the champions visit Gloucester.
But Melville said: "We like the hostile environment and hope we can have the great satisfaction of winning away from home."
With Gloucester just in the top half of the table despite not playing for over two weeks and Wasps toiling in 10th place, there appears to be little meaning to the game.
But Dallaglio denied this, saying: "It's important to finish as high as possible... We've never come lower than seventh in the 10 seasons of league rugby and we want don't want to let down that fine record."
Gloucester - who have won six of their last seven home League games, but have beaten Wasps only three times in 15 meetings - and Wasps both restore international threequarters after long-term groin injuries.
Philippe Saint-Andre, the former France captain, returns for Gloucester after having one short outing in January, also against Wasps, when he suffered a recurrence of his November problem.
Richard Hill, Gloucester's rugby director, said: "Philippe has been struggling for four months and we were not going to rush him after the setback in January."
The Ireland centre Rob Henderson is back in Wasps' midfield for the first time since December, having confirmed his recovery in Paris last Saturday.
Henderson's recall means that Nick Greenstock moves to the wing, while Wasps also start with hooker Trevor Leota and back-row forward Johnny Ions.Reuse content