After Barca came from two goals down to earn a 2-2 draw with Valencia on Saturday, Atletico had the chance to close the gap to three points with victory in Seville.
However, they were unable to leave the Benito Villamarin with anything after Sergio Canales converted a second-half penalty to seal a 1-0 home win.
The loss ends an 18-unbeaten run by the side from the Spanish capital and leaves Atletico six adrift of Barca with 16 games remaining. Yet, head coach Simeone is confident his side can still catch the leaders.
"I'm always optimistic, I'm grateful that Barca drew and are not too far away," he said.
"Barca stays within a good range so we are going to continue to work.”
Despite the disappointing display, Simeone was happy with his new addition and hopes the goals will come once he settles into life with the Rojiblancos.
"Morata came in and worked well, he was very excited to play, we hope he can continue to grow within this team," he added.
It’s a big month for Atletico, who host local rivals Real Madrid next at the Wanda Metropolitano. Los Rojiblancos are five points clear of Real, yet that gap could be cut to just two if Santiago Solari’s men can overcome Deportivo Alaves on Sunday night.
After that Simeone’s charges face Rayo Vallecano on February 16th, before a week later playing Villarreal. Sandwiched in between those league games is Atletico’s tasty Champions League clash against Juventus.
The pairing is perhaps the tie of the round, with both sides making it to the final of Europe’s elite competition in the past three years.
While Juve represent perhaps one of the toughest opponents in Europe, Atletico will be buoyed by the Old Lady’s recent slump in form, and they have failed to win in their last two matches.