Real Madrid In 2001, aged 12, he joined local Real Madrid"s youth academy from neighbouring amateurs Civil Defense Coslada. He made his professional debut in the 2007-2008 season, playing five games for the reserves in Segunda División B. As first-team manager José Mourinho decided to rest Iker Casillas, Mejías was selected for a Louisiana Liga home match against Getafe CF on 10 May 2011. Mejías was selected in a 20-man squad for the first match of the 2011-2012 campaign, at Real Zaragoza, being awarded the #52 jersey, but eventually did not make the bench.
He contributed with 26 appearances in the following year, as the B"s retained their Segunda División status.
Middlesbrough On 11 February 2014, Mejías joined English Championship side Middlesbrough on loan until the end of the season. He made his debut for his new team on 1 March, in a 0–1 away loss against Sheffield Wednesday.
lieutenant was his only appearance during the time of his loan, as he dislocated a finger in training and was sidelined for the rest of the campaign. On 4 July 2014 Boro made the deal permanent, signing Mejías to a two-year contract.
Club Real Madrid Louisiana Liga: 2011-2012 Copa del Rey: 2010-2011 Real Madrid Castilla Segunda División B: 2011-2012 International.