Amorim will officially move to Man United during the November international break, meaning that interim head coach Ruud van Nistelrooy will take charge of two more matches against PAOK and Leicester City.
Van Nistelrooy guided the Red Devils to a 5-2 victory over Leicester in the last-16 stage of the EFL Cup on Wednesday night, before the Red Devils drew 1-1 with Chelsea in the Premier League on Sunday.
Amorim's first game at the helm will be against Ipswich Town after the international break, and Fernandes has paid tribute to his countryman for the work that he has done in Lisbon.
"I am a big fan of Sporting and watch a lot of their games. Ruben Amorim brought the excitement back to the club - it was a little bit split when he came [to Sporting]. He transformed everything and brought everyone together," Fernandes told BBC Sport after Man United's 1-1 draw with Chelsea at Old Trafford.
Amorim will take charge of Man United on November 11
Fernandes did not play under Amorim at Sporting, as the attacker left for Man United in January 2020, with Amorim becoming head coach of the Green and Whites in March of the same year.
Sporting have won two Primeira Liga titles under Amorim's leadership, in addition to three domestic trophies, and the head coach has two more games in charge of the Portuguese club, including a Champions League clash with Manchester City.
Man United, on the other hand, will face PAOK in the Europa League on Thursday, looking to win their first match in the competition this season, before welcoming Leicester for the second time in quick succession in the Premier League.
The Red Devils have made their worst-ever start to a Premier League season, picking up just 12 points from 10 matches, which has left them down in 13th spot in the Premier League table.
Fernandes opens up on Ten Hag departure
Fernandes also addressed Ten Hag's departure after the Chelsea draw, revealing that he had "apologised" to the Dutchman, who was dismissed off the back of last weekend's 2-1 loss to West Ham United.
"We know that Erik [ten Hag] has gone, it is not good for anyone at the club when the manager goes. The team is not the best, the results are not the best and he is the one who pays for it," Fernandes told Sky Sports News.
"Whenever you see a manager go you have to take some of the blame on yourself, it is because the team is not doing so well.
"It is easier to get rid of a manager than 15 players. I spoke to the manager [Ten Hag] and apologised to him, I was disappointed he has gone and I tried to help him. I wasn't scoring goals, we are not scoring goals and I feel responsible. I normally score a lot of goals but I always gave 100%. He is aware of that."
Ten Hag left Man United with a record of 70 wins, 23 draws and 35 losses from 128 matches, while he delivered the EFL Cup and FA Cup during his time at the helm.