Simeone defends Atletico squad selection
Atletico went down 2-0 at home against 10 men in the first leg, when they conceded an injury-time goal after keeper Sergio Asenjo joined the attack at a corner only for Rubin to break away and score in the unguarded net.
"I am in a position where I have to take decisions," Argentine Simeone told a news conference on Wednesday.
"We always look to be competitive and we will be again. Raul Garcia, Adrian Lopez, Cristian Rodriguez and Radamel Falcao are attacking players. We will give it our all even if it is obviously a favourable result for our opponents."
Simeone has seven youth-team players in the squad and left behind regulars such as Spain's Juanfran, Uruguay's Diego Godin, Brazil's Filipe Luis, Turkey's Arda Turan and captain Gabi for the match.
Atletico have made it clear their priority is to qualify for the Champions League this season and they lie second in La Liga. They also hold a 2-1 advantage over Sevilla in the semi-finals of the King's Cup.
Atletico, who play in Kazan on Thursday, beat Athletic Bilbao 3-0 in the Europa League final last May, and also lifted the trophy in 2010 with a 2-1 win over Fulham.