The 52-year-old has called on his players to work as a unit in order to progress to the semi-finals but is well aware that they go into the game at Old Trafford as the underdogs.

United are 12 points clear of Manchester City at the top of the Premier League and Benitez believes a lot of their success is down to their depth in offensive areas.

"It will be a tough game against a good team who are top of the table," he told the club's official website.

"It's an away game for us, so we know it will be difficult but we are confident we can go through.

"If you analyse the squad they have, they have four strikers and two players in each position that could play for any team. They have a strong squad and even when they make changes they keep the quality.

"In attack, they have Chicharito, (Danny) Welbeck, (Wayne) Rooney and (Robin) van Persie, and they can play any of them.

"If you look at the players they have in wide areas and in the middle, especially if they are winning, in the last 20 minutes they still have players like (Ryan) Giggs and (Paul) Scholes to bring on."

Ramires, Victor Moses and Ashley Cole were all rested for Chelsea's Europa League game against Steaua midweek and Benitez is hoping their reintroduction will reinvigorate the side after a 1-0 loss in Romania.

"It's an important competition which Chelsea have done very well in, so hopefully we can carry on," said the Spaniard.

"The good thing is that we have another game so soon after a defeat, hopefully we can do better and win, and we will have five or six players with fresh legs."