Atletico Madrid president Enrique Cerezo is not optimistic that the Court of Arbitration for Sport (CAS) will overturn his club's FIFA transfer ban.
FIFA has already rejected appeals by Atletico and Real Madrid against a one-year transfer ban.
The Rojblancos confirmed they would now present their case to CAS, an independent institution based in Lausanne, Switzerland.
"We have no choice but to acknowledge the [FIFA] ruling and think about our appeal and the possibilities that we think we will have of overturning the decision," Cerezo told Spanish radio Cadena Cope.
The two clubs were found guilty of breaching FIFA rules regarding international transfers of players aged under-16 and, unless successful in their appeals, will not be able to register new players until January 2018.
"I think we have few possibilities of being successful," Cerezo said. "CAS never works favourable to those who appeal. But we have a good group of lawyers that specialise in this.
"We are going to appeal because we don't feel we deserve this ban."
In 2014, CAS upheld FIFA's decision to punish Barcelona with a ban for two consecutive transfer windows for similar offences.
Atletico and Real were both found guilty of "breaching articles 5, 9, 19 and 19bis as well as annexes 2 and 3 of the Regulations on the Status and Transfer of Players."
Cerezo said "We have taken it badly because we haven't committed an infraction or done anything illegal, on the contrar. We need to face this process with dignity and be brave.
"We have to think that in the future we have to do things how FIFA considers it should be done. I think once the ban becomes definite, we will have no choice but to wait until we are able to sign players again.
"The future is difficult but in the past, we've had to overcome difficult times like this one, or even worse."
Atletico spent two seasons in the Segunda Division before returning to Spain's top flight in 2002-03 campaign.
Cerezo, who has been at the helm of the club since 2002, is confident his team can maintain its competitive level despite the ban.
Under coach Diego Simeone, Atletico won the Europa League in two successive seasons before lifting the Liga title for the first time in 18 years in the 2013-14 campaign.
Simeone's side has lost to Real Madrid in the Champions League final twice in the last three years.
Atletico signed five players this summer, including Argentina midfielder Nico Gaitan from Benfica and France forward Kevin Gameiro from Sevilla, while they have seven players on season-long loans at other clubs.
"I think we have a good roster," the 68-year-old Cerezo said. "We have a young squad and then we have players that are playing on loan in other clubs in Spain and in Europe. We expected this decision and our technical secretary has already considered our options."