The Championship club are under some pressure due to interest from several Premier League clubs.
However, manager Neil Harris has spoken about whether the likes of Everton or Brighton will get their hands on the starlet.
Harris told the South London Press: “The game has changed over the last five to 10 years. Premier League clubs now are intent on buying young players.
“We had interest in our young players. That will always be the case at Millwall because we have some excellent players coming through our system.
“Josh is no different to that. What we will be very honest with as a football club, is that we will only sell any player at the right value where we feel we can get the right deal.
“If we don’t get the right offer, then it will go to a tribunal. If it has to be decided by that, then so be it by us.
“Josh is one that we really want to work with moving forward. But if any player wants to move on to pastures new, then we will make sure we will protect the football club.”