The DR Congo international has struggled to get back to his best since a serious knee injury midway through his maiden campaign at Goodison Park.
The Toffees splashed out £25million on the 30-year-old to sign him from Crystal Palace in the summer of a 2016 and he was a regular in the side until his injury in December, which kept him out of action for a year.
When he did return, Bolasie was drafted back into the first-team by then-manager Sam Allardyce, making 17 appearances in the second half of the 2017/18 season.
However, since Marco Silva took charge, Bolasie has not featured for Everton, spending the first half of last season on loan at Aston Villa before moving to Belgian side Anderlecht in January.
Having admitted in the summer that he was unlikely to change Silva's mind, a third loan move now awaits Bolasie having agreed to join Sporting.
The winger will be expected to help the Lions fight for the title in Portugal, while also competing in the Europa League.
Bolasie was the last name out the door as the transfer window shut in Europe on Monday night with Everton having made it their mission to reduce their bloated first team squad this summer.
The club allowed 18 players to move on during the summer, either permanently or on loan, as sporting director Marcel Brands tried to deliver on one of his mission statements of cutting the personnel numbers at the club.
The likes of James McCarthy, Idrissa Gueye, Ademola Lookman and Phil Jagielka all bid farewell to Merseyside and it could have been more had Brands found suitable homes.
Cuco Martina and Oumar Niasse remain on Merseyside but with little prospect of being brought back into the first-team set up by Silva, while Everton were understood to be open to offers for Cenk Tosun and Schneiderlin, despite them having featured this season.
Brands admitted in July that he could see French midfielder Schneiderlin moving on but backtracked on pushing him out the door after Gueye left for Paris Saint-Germain.
With Moise Kean added to Everton's attacking options, Tosun has slipped further down the pecking order and revealed last month he had been in contact with German side Eintracht Frankfurt, only for a move to failed to materialise.
With Brands having previously said he doesn't like to add players in the January transfer window, the focus come the new year is likely to be on moving players on again.