The defender is again being linked with a move away this summer, with Italian champions Napoli keen.
Ahead of yesterday's Club World Cup round of 16 win against Benfica, Maresca said: "All the players who are here with us, I would not want to lose them.
"But, as we have said several times, when the market is open, unfortunately anything can happen. You can buy a player or sell him. Trevoh returned to us in January, if we earned a place in the Champions League among the top four, it is also thanks to him. He helped us a lot."
On Chalobah's future, Maresca added, "He's also played a few games here at the moment. He's with us, we're happy with him. Then, as I said, unfortunately, when the market is open, anything can happen, but not just for Trevoh but for all 25 players in the squad."