Manchester United star Romelu Lukaku was a "bargain" at £75million, according to club great Roy Keane.

Lukaku continued his impressive start to his United career with a brace in a 4-1 Champions League win over CSKA Moscow on Wednesday.

The Belgium international has struck 10 times in nine games in all competitions, helping Jose Mourinho's men make a flying start to the campaign.

Former United captain Keane said signing the 24-year-old from Everton for £75m was a fine piece of business by the Premier League giants.

"He is a good player at a good age. He knows the Premier League. He was a bargain at £75million, it was obvious he was going to score goals," he told ITV.

"He has got off to a good start. He comes across well and seems like a decent character.

"His record at Everton was fantastic and clearly he has gone to a bigger club and better team, who will create so many chances for him, he will get 25-30 goals a season."

However, Keane is eager to see Lukaku deliver in big moments for United, who host Crystal Palace on Saturday.

With league clashes against Liverpool, Tottenham and Chelsea coming up, plus the Champions League, Lukaku will get a chance to do just that.

"The big test will be in the big games. For all top United strikers over the years, [it's] been scoring the big goals in the big games," Keane said.

"We are looking at these outstanding strikers all in great form but the time to judge them will be at the end of the season when the medals and trophies are being handed out.

"It's crunch games when one goal will be the difference."