Ahead of tomorrow's trip to Nottingham Forest, Maresca kicked off his media conference discussing Palmer's situation.
The England midfielder is recovering from a groin injury and Maresca admits he won't be seen until December at the earliest.
He explained, "I was wrong. Unfortunately he needs to be out for six more weeks.
"We try to protect Cole as much as we can. The most important thing is when he comes back, he is fully fit.
"The medical staff are not magicians. We hope six weeks are enough. We need to see it step by step. For sure, he's going to be okay."
On how Palmer is feeling, Maresca also said: "He looks relaxed. He has tried to recover from the injury and doing all the therapy."
On finding a replacement, he continued: "First of all, to replace Cole, it's difficult. Cole is a very important player for us, one of the best in the league. The ones we have, in Cole's position against Liverpool was Malo Gusto.
"The game versus Benfica was Facundo. It depends on the game plan we have. We don't have another player like Cole. Cole is unique."
Other injuries
On other injuries, Maresca said: "Levi (Colwill) and Liam (Delap) are still out.
"Unfortunately Benoit (Badiashile) will be out until December, a muscle problem. We are going to wait for him. Moi (Caicedo), Enzo (Fernandez) and Pedro (Neto) did not take part in the session yesterday. We will see if they can train today.
"Reece (James) is okay, he is fully fit."
Facing Forest
On what he expects from Nottingham Forest, Maresca admits they utilised the international break to prepare to face their new manager Ange Postecoglou.
He said, "When we analyse a team, we consider everything. You have to go match by match. It's always different. For sure, in the international break we watched all the games with Ange in charge.
"Making changes is something you usually plan but it is sometimes dependant on the game."
Maresca will be banned for the game after his red card received at the end of victory over Liverpool.
He added, "It was a big moment for many reasons. Since I joined the club, we never won a game at home in the last minute. It was against the champions of England.
"It was an important moment, for sure. For me, personally, it was a normal reaction in the moment."