Luis twice played for Simeone at Atletico.
He told the Daily Mail: "Take my word for it; it's not easy to play for Simeone. He has no heart.
"He never says to himself: 'Oh, what a pity, poor little player, I need to do this or that'. No. He will decide what he has to decide solely in order to win.
"When he took over in 2011 the team was four points off relegation and he made them Europa League winners the same season.
"He turned them into the monstrous side they are now. That success has one name: Diego Simone.
"About 120 players have been though the club since he arrived. Some came as stars and didn't play, others arrived with no credibility and became stars.
"It's an enormous achievement. And he doesn't waste time, ever. He'll never do a "ah, let's have fun today" session.
"I was a full-back lacking confidence in December when he arrived and the best left-back in the world by January. He's the only person who has managed to get that from me."