Atletico were leading the Champions League playoff first-leg 2-3 before Christos Tzolis struck for the hosts on 89 minutes.
Simeone said afterwards: "How important is the support from our fans?
"We need it not just on Tuesday. We need to be with our fans on Saturday. Giving our all so they show up. We need that energy because we're playing every three days. What matters is winning.
"There's always room for improvement. I think that of all the teams that have played, except for Arsenal, they've competed very well. We had the lead at 2-0, then 3-2... but they play well, they're a dynamic team that plays well. We knew we weren't going to have an easy time. We made mistakes at 3-3."
The Argentine also said: "The match was what we expected. Possibly the toughest opponent in the Champions League. Very young. We knew it wouldn't be an easy game. We controlled the first half.
"We could have scored two goals and had a few counter-attacks. They quickly got back into the game after going 2-1 up. We weren't attacking like we had in the first half. They made it 2-2, we took the lead again, and then came that last goal, which was a misinterpretation of our defensive strategy."