Fellaini has become a useful weapon for Van Gaal, says Redknapp.

Liverpool legend Jamie Redknapp is convinced Marouane Fellaini has become a vital player for Manchester United and has warned Brendan Rodgers' side of the threat he possesses.

The Big Belgian scored the opening goal against Tottenham last weekend and has been impressive - both in attack and defence - for United this season.

On Sunday, Liverpool host Manchester United who are only a point above them in the Premier League table and Redknapp revealed how the former Everton man has become a useful weapon for the Dutch boss.

"If Manchester United are to win on Sunday then he [Fellaini] is going to have a big role to play," the former Tottenham and Liverpool midfielder told the Daily Mail.

"You would never have believed at the start of the season that he would become United’s go-to man but he has knuckled down, worked hard and is now one of Louis van Gaal’s most effective players.

"United have played the third-most long balls this season, so this is not the skilful, free-flowing team of previous years.

"But with Fellaini it is an effective tactic.

“He has gone up for 115 aerial duels this season — far more than any other United man — and Crystal Palace’s Mile Jedinak is the only midfielder to win more headers per game." Redknapp continued.

Fellaini battles with Swansea Jack Cork

"His power in the air is vital for providing knock-downs for the likes of Wayne Rooney and Juan Mata to collect. Liverpool must also track his runs into the box because United will try to find him as often as they can.

"One thing is for sure with Fellaini, you know you’re in a game with him. Martin Skrtel, Emre Can and Mamadou Sakho are big, physical players but they will have a battle on their hands.

“Fellaini gives away on average 2.1 free-kicks per game — that’s the fifth-highest rate in the league and shows you what a fighter he is. It’s not pretty, but it unsettles defences.

"Fellaini's game is not all about power. Like Peter Crouch, he’s portrayed as a bit of a Lurch when actually his technique is good.

Just look at that controlled finish with his left foot to open the scoring against Tottenham.

"He might not be the creative genius to win United titles, but he has become a useful weapon for Van Gaal."

Thinkfootballideas [@Thinkfballideas]