Fellaini, 31, joined United from Everton for £27m in 2014 when he became the first significant signing after Sir Alex Ferguson's departure as manager.
BBC Football has reported that the Belgium international has already passed his medical and the transfer to Chinese Super League club Shandong Lunenis close to being completed.
Fellaini was signed by his former Everton boss David Moyes after making 141 Premier League appearances, where he scored 25 goals and had 14 assists, he also played under Louis van Gaal and Jose Mourinho at United, scoring 22 goals in 177 appearances across all competitions.
However, the towering midfielder who helped United win the 2016 FA Cup final as well as the Europa League and League Cup in 2017 - has featured just three minutes in the league in seven top-flight games under interim boss Ole Gunnar Solskjaer.
Today just got a whole lot better! ???? #MUFC— Manchester United (@ManUtd) January 31, 2019
Meanwhile, Martial, who has scored 10 goals in 25 appearances in all competitions so far this season is said to have signed a new deal that will keep him at Old Trafford until 2024.
The 23-year-old forward has reached a final agreement with the club after months of talks and the rejection of an offer last October.
"Anthony is one of those naturally gifted players that any coach would love to work with," interim manager Ole Gunnar Solskjaer told the club's website.
"For a young man, he has a good footballing brain which, when coupled with his exceptional talent, makes for a player with an exciting future ahead of him.
"This is the perfect club for Anthony to progress his development as a top-class forward and we are all delighted he has signed a long-term deal."