Edson saw red as Forest ranout 3-0 winners on the day.
Lopetegui later said: "After the second goal it was a very different match and it was a hard day for us and for our fans too.
"That's why we have to say first of all sorry for our fans. We are very disappointed today and we have to use these hard moments to push forward and to look forward to the next challenge.
"We know that, even if you are showing control, you have to avoid the counter-attack, you have to defend the crosses better.
"It happened that they scored a goal in this action and after the goal it was more difficult for us.
"We had a very clear chance to level the match before the red card.
"It was a key minute because we were not able to equalise and then straight away it’s a red card. Before the half-time break we were thinking about any changes and looking forward to the second half.
"At the start of the second half we were able to have three or four corners, waiting for our moment to level the match. Unfortunately they scored the second goal.
"We can and we have to do much better.
"You can prepare the team but the players have to take the right decisions and we have to play with eleven men.
"It's one of the situations we can avoid because there was no danger of this. We had a lot of players in our box.
"It is a big advantage for the opponent above all because there is a lot of time in front of you. You are losing the match so it was a bad moment for us and a very good moment for them because they wanted to damage us on the counter-attack.
"That's why in the second half we tried to wait a moment. We were not able to because we suffered the second goal and it was different. That's why I repeat that today is a hard night for us."