The 28-year-old has not been named in the squad for the last 12 matches, and Everton are ready to listen to offers for him.
Niasse joined Everton in 2016 from Lokomotiv Moscow, and has made only 27 appearances in the Premier League since then.
He impressed during his loan spell at Hull City under Marco Silva, but this season it has been a different story.
Niasse has managed only four Premier League appearances from the bench, and he is yet to start a game in the league. The Portuguese manager has preferred Richarlison, Cenk Tosun, and Dominic Calvert-Lewin upfront, and Niasse is now facing an uncertain future at the Merseyside club.
He was close to joining Crystal Palace in 2017 but the deal collapsed at the 11th hour. Cardiff City have reportedly shown interest in signing the Senegal international.