Maresca has confirmed striker Nicolas Jackson won't be seen until April after scans revealed a major hamstring injury.
The Senegal striker suffered the setback against West Ham at the beginning of the month and missed Saturday's FA Cup defeat to the Seagulls.
Asked for an update, Maresca said this morning: "Nico will be out until the international break, probably available after the international break.
"We knew it was a muscular problem but not how important it was. His reaction was good so we didn't think it was a big injury. Unfortunately he had the scan and it is an important one - he will be out for six to eight weeks."
The Blues manager also delivered an update on fellow striker Marc Guiu, while offering hope of his defensive options soon becoming deeper.
"Marc Guiu will be out for a while. Romeo Lavia is in the process to come back with us, Benoit Badiashile exactly the same. Wesley Fofana needs two or three weeks to be 100% fit with us."
With Jackson and Guiu out, a greater burden will fall on the shoulders of Christopher Nkunku, who has struggled for consistent minutes under Maresca this season.
On the importance of Nkunku stepping up to cover Jackson's absence, Maresca continued: "Christo is a solution but not the only solution. I said many times I consider Christo a very important player from the start. Now also with the transfer window closed, everyone is here and he can help us until the end.
"We are working to find a different solution. It can be Christo but also a different kind of player.
"They are different on the ball and off the ball. Sometimes we complain about players but then when they don't play, you realise how important they are. He (Jackson) didn't play against Brighton and then everyone was thinking it is difficult to play without a nine. We know exactly how good Nico is on and off the ball. Christo is completely different on and off the ball."
The Blues meet Brighton just days after being beaten in their FA Cup fourth round tie. Chelsea have also won only twice in their last five League games.
On their current form going into the Brighton clash, Maresca reasoned: "I don't think what we have done can be no good because what we have done is there. I think, unfortunately we are out of both domestic cups. Our journey in the Premier League has been fantastic until today and in the Conference League.
"We will try and finish in the best way we can. Don't forget in the last two years Chelsea have never been in the top four and we have spent this season in the top four. We will try our best to finish where this club needs to be. "
He added, "I didn't say our target was top four - the club never said that. The target was in two years to play Champions League, not in one year.
Regarding meeting Brighton twice inside a week, Maresca said: "I expect a similar game because it is not just against us, but in all the games they try to be aggressive. I expect a very similar game."
Before signing off, Maresca also announced Filip Jorgensen was now his No1 ahead of senior goalkeeper Robert Sanchez. The Spain international has come into question in recent weeks after a series of errors.
Maresca declared: "I said that the Filip solution was also to give Robert some time to recover mentally and physically. But the idea is not to game by game change the keeper. In the last Premier League game we had Filip and in the FA Cup it was Robert. Our keeper at the moment is Filip.
"I spoke with Robert a few days before West Ham where I took the decision to play Filip. I never spoke again with Robert. Filip, exactly the same. They know the situation. This is the situation now and then we will see."