The 25-year-old had been widely linked with a move to Monaco in the latter stages of the transfer window, but the Spaniard remained at the Vicente Calderon.
"We have brought in two major players. [Joshua] Guilavogui and [Toby] Alderweireld are two great additions to squad that was already very strong," he told reporters at a press conference.
"But the signing we have done is to keep Adrian. I am sure this will be his year."
Atletico have won each of their three league matches this season.