Promes was hauled off with a suspected toe injury seconds after Damjan Bohar scored in the 85th minute to cancel out Aleksandr Samedov's opener for the visitors.
After his side played the final minutes of the game without their in-form frontman, Carrera revealed that the decision to substitute him was made in error.
"Promes' substitution was a mistake," Carrera told reporters.
"I wanted to replace another player, but he [Promes] pointed to his foot and I thought he had a problem. But it wasn't so."
Promes was one of a number of players to go close to scoring for Spartak on the night as they sought to make a winning return to the Champions League group stage following a five-year absence.
But Carrera paid tribute to the perseverance of the Slovenian champions, who fought to the end for a famous result.
"We didn't respond well after we scored and that led to the equaliser," said Carrera.
"We always play to the best of our abilities. We want to win at all our matches. There are five matches left and everything is still possible.
"We played our game, we had enough chances to score, but the result is fair. Both teams deserve a point."
After seeing his side snatch a point in the dying minutes, Maribor coach Darko Milanic said he did not want the final whistle to blow and he singled 25-year-old midfielder Bohar out for praise.
"We saw a great match, excellent, even. I am very satisfied," said Milanic. "We had lots of chances. We managed to equalise, we showed great character.
"I thought we could crush them. I wanted to up the pressure and I wanted to keep on playing. We were tactically very good when they [Spartak] had the upper hand.
"Bohar is a specialist for these European matches. He is very good at finding spaces. He was very solid.
"Of course one wants always to achieve even more, but we are really satisfied with this result."