The Red Devils were down 2-1 at Old Trafford when the half-time whistle blew.
Whatever was said worked as United romped to a 6-2 victory over their Italian opponents.
Fernandes told MUTV after the game: "The manager and the players, we also talk, as we said about keeping calm and doing the right things, play easy football, quick football, one and two touches and keep the head fresh and calm.
"Don't go mad, don't try to win the game in the first five or 10 minutes of the second half because we know we had a long way to arrive at the final.
"Like I said, before at half-time we knew we had three halves to play so the second of the four halves we ended very well. And we have to do the same in the two halves we have left to play."