The Italian had said after a 4-3 League Cup win at Wolverhampton Wanderers on Wednesday that Delap was "playing the game for himself" and called the sending off embarrassing and stupid.
"I spoke with Liam, he knows everything, he's aware of the situation, he knows that he made a mistake. Full stop. No more than that," Maresca told reporters ahead of the Premier League trip to Tottenham Hotspur on Saturday that Delap will miss.
"Straight after the game, in the changing room, he apologised to everyone."
Chelsea have had five red cards in their last nine matches and Maresca conceded some of them were avoidable.
"It's something we need to learn, something we need to do better. For sure in the future we will be better on that," he said.
The manager suggested his comments about Delap had been misunderstood. "I'm not from England so sometimes when I try to translate from Italian to English, sometimes it's a bit different," he added.
"Liam, on the pitch, is more focused on his battle with the central defender than the rest. This was what I was trying to say after the Wolves game.
"I know that Liam will be a fantastic player for us but there are some things, like the rest, that he needs to improve."
Maresca said Chelsea would still be without Cole Palmer but Enzo Fernandez, Moises Caicedo and Joao Pedro were all available for the Spurs game.
Chelsea are ninth in the Premier League, three points behind third-placed Tottenham.