So much so that he still owns one of the vests he used to wear during matches.

"Every time I see a ball boy, I see myself in him," the striker said. "And when I was not a ball boy, I was in the stands watching Atletico. I used to dream of one day being on the field and playing."

The dream is coming true for Morata.

Atletico signed him on Monday to an 18-month loan from Chelsea, ending his miserable stay in English soccer following a club-record move from Real Madrid for $75 million.

The 26-year-old Spaniard passed his medical exam on Sunday in Madrid.

Morata is returning to the club where he also started playing as a child.

"I'm very happy and proud to be here," he said. "I can't wait to start practicing with my teammates and to start playing."

Morata had his first training session with Atletico on Monday.

He played in Atletico's youth program before joining Real Madrid's academy in 2008. He eventually became a first-team player for Real Madrid and helped it win two Champions League titles.

His links to Real Madrid caused some Atletico fans to protest against the transfer. Part of the crowd attending the team's 2-0 win over Getafe on Saturday criticized Morata's signing.

Financial details of the transfer were not immediately released.

Morata spent a year-and-a-half with Chelsea, his last appearance on Jan. 5 in the FA Cup where he scored both goals against Nottingham Forest in a 2-0 win.

Chelsea was the first big club where Morata was signed as the first-choice striker — he was primarily a backup at Real Madrid and Juventus. He scored seven goals in his first seven competitive games before finding the net only eight times in his final 40 games last season.

Chelsea manager Maurizio Sarri called Morata "a little bit fragile from the mental point of view," and said he needed a new striker to cure Chelsea's shortage of goals. The London team has since brought in Gonzalo Higuain on loan from Juventus.

Morata was not a regular starter under Sarri, and scored five times in the Premier League.

He heads to Atletico at the request of coach Diego Simeone, whose forwards include Antoine Griezmann, Victor "Vitolo" Machin, Nikola Kalinic and Diego Costa. Vitolo and Costa have been out of action because of injuries.

Morata has 27 appearances and 13 goals for Spain. He played in the 2016 European Championship in France, but missed out on the squad for the 2018 World Cup in Russia because of poor club form.

The striker has 82 goals and 37 assists in his career.

A day before Morata's arrival, Atletico said it agreed to loan Portugal forward Gelson Martins to Monaco for the remainder of the season. Martins has one goal in 12 appearances this season.

Atletico trails Spanish league leader Barcelona by five points. It faces Juventus in the last 16 of the Champions League on Feb. 20.