Like most opponents O'Neil has marvelled at the form of the Portuguese winger this season and believes his skills have helped him surpass Thierry Henry and become the best Barclays Premier League player ever.

And O'Neil admits that often no amount of planning and preparation can make a difference when it comes down to facing players of that calibre on the top of their form.

O'Neill said: "We will try to stop him to the best of our ability but sometimes when you come against top players like that they do things that are unstoppable.

"It has been an unbelievable season for Ronaldo. In terms of an all round game the best was probably Thierry Henry two or three seasons ago at Arsenal but Ronaldo this season just about tops it for me."

O'Neil, who has been one of the success stories of Boro's unpredictable season since his move to the north-east from Portsmouth, believes confidence levels have been restored in recent weeks.

Even last week's narrow defeat to Chelsea at Stamford Bridge served to show some positives about Gareth Southgate's side and O'Neil says Boro's belief will be apparent against United.

He added: "We're going to have a go at them. It's difficult to take the game to a side like United but when we get the opportunity we're not going to sit back and let them come and beat us."

Boro ought to be mathematically safe if they pick up at least a point against United but O'Neil is adamant the season will not be over as they strive to finish as high up the league as possible.

"We've been a league with eight other teams all season and it would be great to finish on top of that little league," added O'Neil. "If we finish well and can catch Tottenham that would be even better.

"We are not as far up the league as we ought to be this season but there are positive signs and I have enjoyed it up here. There is definitely a lot more to come from this squad."

Boss Southgate is without Mido, who has been ruled out for the rest of the season with a hernia problem, and foot injury victim Robert Huth, although Fabio Rochemback returns from suspension.

Southgate said: "As a manager you are looking at all your players and staff to see how they approach the last six games. It will tell us who can take us forward and what changes need to be made.

"People will get opportunities in this period but we have got to finish the season strongly. We are not yet mathematically safe and we still have to get results to ensure that."