Simeone replaced Joao Felix with Alvaro Morata in the second half of the game against Celta Vigo and explained his move by pointing out that there is no obligation to keep a player on the field for the duration of the match.
"The players do not have a contract [stating] that they have to play the [whole] 90 minutes," Simeone said after the match.
"Joao [Felix] had done well until then and I decided to replace him even though he played a good game."
The Argentine tried to explain the reasons behind Atletico's unconvincing performance.
"We came from putting in a big effort on Wednesday [against Juventus]," he added.
"The first half was even, but in the second we tried all the ways to find a goal.
"We couldn't do so, Celta defended very well and we were not good.
"We also passed against Juventus the anxiety and ambition of wanting to win which made us hurry, but I am left with positive impressions."