The Belgian striker is still short of match sharpness and confidence since being reinstated into the starting XI following his fall-out with the Blues boss after criticising his tactics in an Italian interview.
And Lukaku spurned a couple of good chances to score in the 2-0 win over Tottenham on Sunday.
Chelsea striker Romelu Lukaku looked laboured in the victory Tottenham on Sunday
Redknapp told Sky Sports: 'His biggest challenge right now is probably Lukaku.
'I think he's got to get that right because I watched him today and again there was some