Diego Costa's return to form and fitness could prove more valuable for Atletico Madrid than their eight new signings, according to team-mate Saul Niguez.

Five pre-season goals - including four and a red card in the stunning 7-3 thrashing of rivals Real Madrid - suggest the controversial striker is getting back to his best.

He managed just 16 appearances in LaLiga last term due to a combination of injuries, Alvaro Morata's arrival and a season-ending eight-game ban for insulting a referee.

Costa still has one match of that suspension to serve but looks to be enjoying a new lease of life after two lean campaigns.

"Diego looks great to me," Spain midfielder Saul told Spanish radio station COPE.

"I love it when he's like this, [because his attitude is] infectious. He's a player we need at all times.

"I love that he defends his team-mates as he did against Madrid, that he fights for the shirt and I think that if Diego Costa is at his best level he will be the best signing we have."

Atletico need Costa to remain among the goals as they seek to compensate for the loss of Antoine Griezmann, who scored no fewer than 15 in any of his five LaLiga seasons with the club.

Though his departure for Barcelona had long been expected, Saul admitted to being taken aback.

"I was surprised," the 24-year-old said. "He was a very important player and for him to leave is difficult. Atleti is above any player and when he wore the shirt there was nothing to reproach him for.

"He may not have left in the best way but we shouldn't crush him either."