Diego Simeone believes Atletico Madrid will be held back from achieving their aspirations this season if they cannot address their problems in defending against aerial threats.

Atleti let a lead slip to lose 2-1 to Athletic Bilbao in the semi-final of the Supercopa de Espana in Saudi Arabia on Thursday.

The LaLiga champions looked set to face city rivals Real Madrid in the final at King Fahd Stadium on Sunday after Unai Simon's unfortunate own goal put them in front just after the hour mark.

Yet the holders mounted a great fightback in Riyadh on Thursday, Yeray Alvarez rising to head in a corner from Iker Muniain after 77 minutes.

Teenage substitute Nico Williams won it for Athletic nine minutes from time, finishing clinically with his left foot from inside the penalty area after Simeone's side failed to deal with another corner.

Jose Gimenez's red card for a dangerous challenge on Inigo Martinez added insult to injury for Atleti.

There were elements to the performance that pleased Simeone, but he fired a warning that his side are unlikely to challenge for trophies unless they can solve their issues in the air.

"There are things that can't be hidden. The team doesn't have defensive strength in aerial play and that takes away from us the possibility of having better games and better opportunities to be higher up in LaLiga and to stay in this competition," said the Atleti coach.

"This isn't the time to talk much. Everything looks much worse with the result, but there were good things. Joao [Felix] played a good game, [Angel] Correa worked, [Rodrigo] De Paul did well when he came on, [Mario] Hermoso's game was very good, Marcos [Llorente] was able to play for 45 minutes coming in with an overload in his glute, and we have to improve in training, on a day-to-day basis and get what comes to us from that."

Asked if it seemed his team had finally reached a point where they had stopped believing, he replied: "It's an opinion more than a question. I hear that as an opinion.

"We believe in the work we do. We're trying to improve. Since the Rayo [Vallecano] match [a 2-0 win on January 2], I think we've played good games, but we need to improve something very obvious that makes us lose points, [league] positions and stops us being in finals. It is up to us to improve that and increase the aggressiveness in the areas."

Llorente started the game at right wing-back before being replaced by Renan Lodi at half-time, but the pair between them only provided one cross from open play throughout the contest.

It laid bare the concerns Simeone has over that position following the sale of Kieran Trippier to Newcastle United.

While he is happy with the options at his disposal, with Sime Vrsaljko another who can play the role, Simeone said the club were exploring options in the transfer market.

"We have Vrsaljko as a replacement. He can play there. The club is working with what can be done in pursuit of the benefit of the club and of the team," he said.