That is according to The Sun, who claim the 19-year-old has been the subject of interest from Chelsea scouts in recent weeks.Â
The 19-year-old is yet to feature for the League One outfit's first-team since he joined the Lions from non-league side Brentwood Town last summer.Â
But despite this the defending Premier League champions have apparently been alerted by Mbulu's impressive performances at Under-21 level.Â
Mbulu, who recently had a loan spell at Ryman Premier League side Canvey Island, has been compared to Manchester United centre-back Chris Smalling.Â
Smalling was handed a professional contract by Fulham in 2008 when playing for Maidstone United before sealing his big-money move to Manchester United.
And like Smalling, Millwall boss Neil Harris is hoping to unlock Mbulu's potential after signing him.Â
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"He is a young guy who has been playing non-league football without any professional coaching or full-time training," Harris said.
"We hope to realise the potential that we have seen on the training pitch and in a couple of pre-season games.
"Christian was recommended to us and we want him to be given every opportunity to progress further."Â