The pundit has been discussing the Everton forward.
Indeed, the former midfielder and current pundit believes the Belgian is talented enough to produce his best week, week out.
At the moment, though, Redknapp feels the 22-year-old is not being consistent enough - and has described the 'trouble' with the Everton target man.
Redknapp told the Mail: "In the past I've been critical of Romelu Lukaku. The only reason for that is frustration, because he can be so good. On his day, Lukaku is a monster. He's bigger, stronger and quicker than almost every centre back he plays against.
"He's devastating in the air and has great subtlety to his game - he's not just a battering ram. Sometimes I find myself thinking: 'My god, you've got everything.' The trouble is, I'd like to see it more often."
Redknapp was full of praise for Lukaku's achievement of reaching 50 Premier League goals despite his demands for more from the 22-year-old.
Former Everton striker Victor Anichebe took to Twitter to congratulate the Belgian on Saturday night, too. Intriguingly, Anichebe got Lukaku's age wrong!
He thought the Toffees forward was 23 - which sums up just how young he is but, equally, how long he's been around despite his young years. Redknapp wants the Everton target man to produce more often, though. And imagine how many goals Lukaku would get then!?
Everton were very much on song against Aston Villa on Saturday afternoon and travel to Bournemouth for their next Premier League clash, during which Lukaku will no doubt fancy his chances of scoring again.