Atletico welcome Barcelona to the Vicente Calderon for the second leg on Wednesday, with the two sides currently level at 1-1 from the first leg last week.
"This is best time of our lives," Gabi told reporters on Tuesday.
"We are not tired. We want to compete at our best level, to give our best. The key to the match will be remaining concentrated throughout the 90 minutes. It's not easy to stop players like them.
"We are looking to be as concentrated as possible. Our minds are not focused on drawing this game. We haven't even thought about [a penalty shootout]."
Atletico have not yet been beaten in the Champions League this season.