Palmer went into Sunday’s game on the back of an eight-game goal drought across competitions, his longest such run in a Chelsea shirt.
“Cole, yesterday didn’t train because he didn’t feel well and during the night he didn’t feel well,” Maresca said.
“This morning, he woke up and said to me: ‘I want to be on the pitch because I want to help this club and this team play Champions League’.
“In the last two days, he was completely out with fever and diarrhoea. In the last 48 hours he didn’t train and was very bad, with a fever and this bad feeling.
“But this morning, he asked to play the game and this shows how the players want to bring this club where it belongs.”
Cole Palmer saw his penalty saved by Mads Hermansen
With a more challenging fixture list ahead, starting with next weekend’s away trip to Arsenal, though, Maresca insists he is confident his talisman will soon be back to his best.
“The Leicester keeper is brilliant and Cole is going to score more penalties and miss more,” he added. “The people need to understand the effort he made to be there. Cole is a top player. Everything is normal now.”