The 25-year-old arrived at Old Trafford on Thursday in a deal which could be worth up to £68m after add-ons.
Fernandes has been with the team from the Portuguese capital since June 2017 following a move from Serie A outfit Sampdoria.
The Portugal international has contributed 63 goals and 52 assists in 137 appearances for Sporting Clube de Portugal, winning the Portuguese League Cup and Taca de Portugal in the process.
The former Udinese man has played 19 games for the Portugal Senior team and was part of the squad that won the inaugural UEFA Nations League against Netherlands in 2019.
Minutes after signing for the Manchester-based club, Fernandes admitted he has been in love with the club since watching Portugal superstar Cristiano Ronaldo during his days in England.
"My love of Manchester United really started when I used to watch Cristiano Ronaldo play and ever since then I have been a big fan of this great club," Fernandes told United's website.
"For me to now play for Manchester United feels incredible, I have worked hard to get to this moment and I can promise the fans that I will give everything for the badge to help bring us more success and trophies.”
"I want to thank Sporting for everything they have done for me. It is surreal to hear the nice words that have been said about me from players that used to play for this team.”
"A massive thank you to Ole and everyone at Manchester United for the trust they have shown in me and I can't wait to start to repay that on the pitch."
