The Belgium international emerged as a key figure for the Red Devils in 2016-17, with Jose Mourinho often turning to him in big games.
Fellaini also saw the option of a 12-month extension to his contract taken up in January, with that agreement taking him through to 2018.
He could, however, be set to depart Old Trafford during the current transfer window, with United pursuing other midfield targets and Turkish giants Galatasaray willing to offer him a new challenge.
Ergun told Ajansspor: "Fellaini will leave Manchester United and he is now on our radar.
"There will be surprises, we are in talks with Fellaini.
“We have made an approach, we are close and if we get Fellaini we will end our pursuit of [Villarreal's Alfred] N'Diaye.
“We need a player like Fellaini who can move around in midfield."
Fellaini made 47 appearances for United in all competitions last season – his highest tally since signing from Everton in 2013.
He helped the Red Devils to three pieces of silverware, with Mourinho starting him in the Community Shield and Europa League final and bringing him off the bench in an EFL Cup final victory over Southampton.
Despite being a favourite with his current boss, the 29-year-old has struggled to win over a sceptical fan base since making a £27.5 million switch to Old Trafford.
If he is to move on, though, then he will do so having made 133 appearances for United and netting 15 goals.