Rio Ferdinand on Cristiano Ronaldo's importance as Man Utd face Atletico Madrid

Former Manchester United defender Rio Ferdinand believes Cristiano Ronaldo remains the club's key man ahead of Tuesday's Champions League clash with Atletico Madrid - and has insisted the Portuguese forward 'owns the competition'.

37-year-old Ronaldo is the top scorer in the history of the Champions League, and has on a number of occasions already this season bailed United out of difficult situations - essentially dragging them through the group stages and into the last 16 with late goals.

His hat-trick against Tottenham in the Premier League on Saturday was another example of his ability - even while the goals had dried up for him in previous fixtures.

United have struggled for performances for most of the season, with or without Ronaldo, but face Atletico at Old Trafford with Ronaldo himself set to start after his weekend performance.

BT Sport pundit Ferdinand, who was speaking exclusively to 90min ahead of the match with Atletico - airing live on BT Sport 2 - pointed to Ronaldo and another arrival last summer, Jadon Sancho, as two players who will be decisive to United's progress.

"Jadon Sancho, form wise, is in the best form he's been in in a Man Utd shirt, and I think there's loads more to come from him," Ferdinand said. "He's had the adaptation time and I think we're seeing the benefits of that now. He's fitter as well. He's one of those in recent games you've looked to for that spark, that bit of quality.

"But you can't go into a Champions League game being Man Utd in the way they are, in the form they're in, without Cristiano Ronaldo and what his competition means to him.

"Without him, they're not in this game. They don't play this game - they're already packed up and in the Europa League. He's been the most decisive player in the Man Utd team in this competition.

"There's certain players that when they go to get into a certain competition, whether it's FA Cup for certain people or whatever [it is], the Champions League is Cristiano Ronaldo - the most decisive player that's ever played in the Champions League.

"He owns this competition, and the numbers tell you that."

For United to own the competition, they'll need to raise their levels of performance after a stuttering (at best) season so far. United managed a 1-1 draw in the reverse leg in Madrid, but Ferdinand believes the energy levels need to increase in what will be a difficult encounter.

"They need to match them - in terms of energy and work ethic," Ferdinand added.

"They have to be tight, and a close unit at the back. They've got to communicate, and then they've got to be clinical and decisive when they get the chances up front - because they will create chances. We saw against Manchester City recently, as bad as they played and as bad as the result was, they still created chances in that game.

"We know they've got players capable of doing that, but they've got to be a cohesive group, a cohesive unit playing together, and not play in moments."

United are struggling to qualify for next season's Champions League despite Saturday's win over Spurs, though did see domestic rivals Chelsea struggle for form in the middle of last season before a change of manager led them to the title of 'Champions League winners'.

While it's quite the stretch to suggest it could happen to United, Ferdinand admitted there's an example to follow.

"That's got to be the blueprint for the rest of the season, hasn't it? Chelsea were in a position where a new manager comes in, the team changes and their fortunes totally get turned around - and that's got to be an inspiration for this team. Nobody gave Chelsea a chance in hell of winning the Champions League, and they went on to win it in style.

"Can Man Utd do that? We'll have to wait and see.

"They have to improve in terms of their performances. They'd have to start getting consistent through the 90 minutes, I think that's been the biggest problem.

"You look at the teams that [Ralf Rangnick] has played against, it's been quite favourable in terms of their level of opponent - teams that you'd expect them to win against. But the performances I think have been the biggest disappointment for everybody, which is why there's a little bit of a negative vibe around a club.

"The performances have been very Jekyll and Hyde. For 40 minutes, half an hour of a game, you think actually this looks like something very positive, [they're] very confident, look at them...and then all of a sudden it just kind of blows up in their faces and it capitulates in terms of performance. So that's where they're at the moment.

"That's probably one of the most frustrating things. Forget about if Ralf Rangnick thinks 'x' player is good enough, or he's not, or he isn't the right character, or he is - the performances of the team haven't had any level of consistency throughout.

"I think it's a great opportunity [to salvage a disappointing season]. You get a draw in Europe away from home and you bring in a team back to Old Trafford, you are mightily confident. You're sitting there rubbing your hands and saying, 'yes, this is us'.

"But it's very different at the moment. There's probably a little bit of anxiety creeping in for the fans and the players thinking 'will we get through here? we're not completely sure, we don't know what kind of performance we're going to put out...' because that's what the last couple of months have shown us. No one knows what Man Utd are going to come out of the traps at Old Trafford.

"But it's an opportunity to change the fortunes of the season. It's an opportunity to change confidence levels, it's an opportunity to start some sort of momentum, if they can, and that's what you need at this stage of the season. You need a game, you need a performance. A mediocre, lucky win won't be enough to change the confidence of this team.

"You need it all to hit - you need the result and you need a performance to back that up to start going 'actually, guys, there's something maybe for us at the end of this season'. And then that togetherness, it starts building through results and performances."

You can watch the full interview with Rio Ferdinand on 90min's Manchester United podcast 'The Promised Land' - subscribe now.

BT Sport is the exclusive home of UEFA Champions League football. Watch Manchester United v Atletico Madrid on Tuesday 15th March from 7pm live on BT Sport 2, online and on the BT Sport app. For more info, visit btsport.com.