He stepped up his fitness battle after coming through an hour for the Reds' Under-21 team against Middlesbrough last Friday.
"Lucas came back and played an hour last week in an U21 fixture so he could be available sooner rather than later," Marsh told the club's website.
"Everyone is looking forward to welcoming him back and getting him on the pitch in a first-team shirt.
"He's not far away at all - if he gets a good week in training while we're away in London, he won't be far away from being included in the next game or two.
"Fortunately we're blessed with a lot of central midfielders so there's no rush to get him back in - when the time is right I'm sure the boss will put him in when he thinks it will benefit Lucas and the team.
"He's a Brazilian international, he moved away from home when he was very young - he is a very mentally strong player. We're looking forward to having him back."