The 25-year-old, who has been with Chelsea since the age of eight, now looks set to leave Stamford Bridge this summer after he was left out of the travelling squad for the club's pre-season fixtures in the United States this summer.
Chelsea are understood to be open to selling Chalobah for a figure in excess of PS30 million, while the defender is said to have already attracted interest from multiple Premier League sides.
Chalobah, who still has four years remaining on his current contract with Chelsea, made 13 Premier League appearances last season after missing the first six months of the campaign with a hamstring injury.
The defender is said to be stunned by the decision but Maresca claims thatstrong competition for a place in Chelsea's defence following the arrival of Tosin Adarabioyo on a free transfer from Fulham, plus the return of Wesley Fofana, who missed all of last season as he recovered from ACL surgery, are the reason behind the decision to omit Chalobah from his pre-season squad.
Asked about Chalobah's situation in his first pre-season press conference in Santa Clara on Tuesday evening, Maresca said: 'First of all, from my point of view, it's always sad to leave players out, that can be out of a pre-season, or can be out of the squad or out of the first eleven because in the end they all work for the same target, that is to be part of the same team.
'It's a sad decision but we have to take the decision.'
Maresca also stressed that he was unable to highlight any potential errors made during Mauricio Pochettino's reign which could have contributed to Chelsea's multiple injury problems last season.
'I always say the same, it's already difficult to judge a situation when you are inside, imagine when you are not here,' Maresca said when asked about Chelsea's issue with injuries under Pochettino.
'So I don't know what kind of problem they had the last year or two years ago.
'The only thing I can say is fortunately we started two weeks ago, we didn't have any problems, any injuries, and we're going to try to also manage that kind of situation that in the past has been a problem.
'But as I said, I don't know the reason why they had many injuries in the past. We are focused now on trying to create personal work prevention, these kind of things, to avoid injury.'
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