On Sunday he made his debut for his new side but Real Betis dented Atletico’s title hopes with a 1-0 win.
Diego Simeone’s side could have closed the gap on league leaders Barcelona to three points but instead lost for the first time in 19 league games.
Supporters took to Twitter to explain that the defeat was down to the ‘Morata effect’.
One user wrote: ‘Coincidence? I think not,’ while another wrote on the social media platform: ‘Morata’s been carrying around his bad luck everywhere. Poor Atleti will suffer now. #Morataeffect.’
Another Tweet read: ‘This is just the beginning. They soon stop scoring. Morata effect… lol.’
Sergio Canales buried a penalty midway through the second half just minutes after Morata had a penalty shout waved away.
The Chelsea loanee was brought down by Zouhair Freddal but the referee did not point to the spot and opted not to use VAR.