Fernandes, who scored 19 goals and provided 19 assists in 57 matches across all competitions for United last season and was awarded the club's Player of the Year title, was rumored to be moving to Saudi Pro-League club Al Hilal earlier this year.
However, the 30-year-old mentioned last month that he had contemplated the transfer but ultimately declined to continue playing at the highest level.
When asked about Fernandes' significance to the team, Amorim informed reporters after the victory: "It was evident last season, as seen in the goals and assists. But it’s not limited to that.
"I believe he now has more players to assist him in leading the group, which is beneficial. He is our leader and extremely significant, both on and off the field. He sets an example.
"At times, the issue is that he becomes frustrated and loses a bit of focus on his responsibilities. Occasionally, he wants to assist his teammates too much, which isn't always the best approach. They need to perform their roles, and Bruno must, for instance, wait for the ball."
United have acquired Matheus Cunha and Bryan Mbeumo thus far in the transfer window, with Amorim stating that these additions would alleviate some of the pressure on Fernandes in attack.
"Last year, I occasionally felt that I was pushing him back to gain more possession during build-up, and we missed Bruno near the box," Amorim added.
"With the different attributes of Bryan (Mbeumo) and Matheus Cunha - and I really appreciate Kobbie Mainoo's style of play - he (Fernandes) will receive more support this season."