Romelu Lukaku was a bargain at £75m... but the Manchester United striker must deliver against the best to really prove himself at Old Trafford, insists Roy Keane

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Romelu Lukaku is a top quality striker but he must score against the best sides in the world to really prove himself in a Manchester United shirt, according to Roy Keane.

Lukaku, who arrived at Old Trafford for £75million from Everton in the summer, has scored 10 goals this season for United, including two in the 4-1 win over CSKA Moscow on Wednesday night.

But while Keane believes the striker is providing value for money he is expecting more when it really matters.

Former Manchester United midfielder Roy Keane praised Romelu Lukaku on Wednesday

Lukaku celebrates scoring his first goal of the evening for United against CSKA Moscow

'He’s a good player, a good age, he knows the Premier League,' said Keane, who played 12 years for United.

'He was a bargain at £75m. He’s got off to a good start, and seems like a decent character.

‘You look at his record at Everton, and he’s gone to a much better team. It’s so obvious he’s going to get 25-30 goals this season.'

The Belgium striker scored a brace to move him to 10 goals in a United shirt this season

Jose Mourinho's side are yet to play any side currently in the top 10 of the Premier League.

Keane insists Lukaku's biggest challenge in front of goal for United is yet to come - despite playing and scoring against Real Madrid in the European Super Cup.

He added: ‘The big tests for Lukaku will come in the big games. United haven’t had to play anyone big yet, while you can only beat what’s in front of you. 

'The big test for all United strikers is whether he can score the big goals in the big games.

United manager Jose Mourinho speaks to Lukaku following United's victory in Russia