The Brazilian left-back won the Premier League and League Cup during one year with the Blues after signing for £15.8m.
But with just 15 league appearances, Luis rejoined Diego Simeone in the Spanish capital the following summer.
Luis has pinpointed how pre-season fitness, struggling to adapt to English football and Cesar Azpilicueta’s form for his inability to hold down a starting role under Mourinho.
And while there are no regrets, Luis concedes he felt let down by Mourinho for a lack of opportunities.
Luis detailed his struggles at Chelsea in an interview with the Mail: “When I was on the bench for the first game of the season I knocked on Mourinho’s office door and said: ‘Why did you bring me here? Why didn’t you just leave me at Atletico?’
“He said that he didn’t feel as secure defensively with me in the team as he did with Azpilicueta. He said I had to win my place. I couldn’t expect that because of my name I was going to be first choice.
“He was right. I wasn’t playing well. But I also think you have to be on the pitch to improve. I never regretted the move because I was at one of the biggest clubs in the world but everyone wants to play!
“At the time I felt betrayed for want of a better word. I did not want to work for Mourinho for another year. But it was not his fault. We won the final and I have the medal at home!”
Luis’ former clubs face each other in the Champions League on Tuesday with the Blues travelling to Bucharest for the first leg of the last 16 tie.