The Blues have made 11 signings so far this summer which has seen the senior squad swell to more than 40 players.
Earlier this week, Maresca said England internationals Raheem Sterling and Ben Chilwell were part of a group of about 15 players told to train away from the main first-team group.
“At the moment, with the squad that we have, I am working with 22, 23 or 21 players – not with the 42 players, otherwise it is impossible,” Maresca said.
“It is impossible for any manager in the world to make a session with 45 players. It’s impossible. You cannot do that.”
Sterling was left out of Maresca’s first Premier League squad, for the 2-0 home defeat by Manchester City on Sunday, while he also missed their Europa Conference League play-off first-leg win against Servette on Thursday.
The forward’s representatives said in a statement on Sunday that they wanted “clarity” over Sterling’s future at the club, since when Maresca has said he had already made his position clear.
BBC Sport understands Crystal Palace are interested in the 29-year-old, while there are reports he has been offered to Aston Villa.
England midfielder Conor Gallagher has left for Atletico Madrid – in an unpopular move with some sections of Chelsea’s support – with fellow home-grown star Armando Broja set to join Ipswich in a loan move with an obligation to buy.
Several other players appear to have uncertain futures, including defenders Chilwell, Axel Disasi and Trevoh Chalobah, and midfielder Carney Chukwuemeka.
“I just communicate the players that I like and the players I don’t like and because there is one week, or 10 days, left of the transfer window, hopefully we can find solutions for all of them,” Maresca said.
“When you find solutions, everyone is happy. When you don’t find a solution, then you can create some problems.”
The transfer window closes on Friday, 30 August.
