Jamie Carragher and Roy Keane clash over 'panic signing' Cristiano Ronaldo

Cristiano Ronaldo's return to Manchester United has proved a mixed bag, so it was no surprise to see Jamie Carragher and Roy Keane disagree over his impact at Old Trafford this term.

Ronaldo returned to the club last summer to much fanfare 12 years after departing for Real Madrid but ahead of Liverpool and United's clash in the Premier League on Tuesday, Jamie Carragher believes United made a mistake signing the the Portuguese star.

Speaking with Keane in face-to-face discussion from LADBible, Carragher claimed part of the mistake was due to Ronaldo not being enough to push United into a Premier League title fight, with the Red Devils down in fifth this term and 20 points off the summit.

Manchester United should be buying someone who is 27 not 37 - who's the next Ronaldo?, Carragher said.

'It just smacked of where the club was. I always felt it was never going to push them closer to the Premier League title.

If you watch Ronaldo and if you are judging all of United's outfield players, he's still been one of the best, if not the best. For Ronaldo to still play at one of the best clubs in the world at 37 and still have an impact - it's unbelievable. But for United to buy Ronaldo, I just thought it was a joke.'

'It was either a panic because they thought [Manchester] City and whether they were kidded by that or this thing about getting Ronaldo back and everyone's excited, the social media - I thought it was a bit embarrassing.'

Keane though believes United made the correct call at the time in resigning the fan favourite.

'I still think it was worth the gamble,' he countered.' At the bigger picture it's not a great signing because of his age. I still think he can bring something to the party. I think he has.

'Whatever has gone on around him hasn't been good enough but I think Ronaldo could have shown better leadership skills. He's still showing moments though.'

The two rivals also disagreed on whether Pep Guardiola could surpass Sir Alex Ferguson as the greatest Premier League manager of all time.

However it was former Liverpool star Carragher who believes the legendary Manchester United boss is untouchable.

'I think Pep Guardiola is amazing,' Carragher said 'He will finish his career as the most successful manager in football. The reason I would still go with Ferguson is not just to do with the Premier League.

The one thing Pep hasn't done is win with an inferior team or when up against the odds. Managing the great players and teams is obviously a skill in itself but Jose [Mourinho] won with Porto, Ferguson with Aberdeen, Klopp at Dortmund - I'm not saying these mangers are better than Guardiola. But in terms of Ferguson in how how long he was in the Premier League and where they were when he came in and becoming the guy to win that first title and keep it going, I'd still have Ferguson ahead of Guardiola.

Keane though believes, Guardiola has simply been smart in working with the best players and doesn't need to prove his worth at a lower level.

The former United captain added: 'He's worked with the reserves and Barcelona first team and people go "he's at Barcelona and it's easy to win" but other Barcelona managers haven't won that much - loads have been sacked. And of course he's clever, going to Bayern Munich and City. He wants to work with the best.'

However, the duo did admit that Keane's former United team-mate and Carragher's fellow Sky colleague talk too much, with both admiring the former England defender's multi-tasking skills.

'I've never met anyone like Gary Neville, Carragher said. 'He's got a million things going on at once. At 4.10pm we have to get for kick-off at 4.30pm. We have to get to the lifts, sort out our microphones, and headsets. We have probably got two to three minutes and he has got his laptop out and I think he has gone on a stat pack.

'So I had a look and he is sending an email over his hotel! I'm thinking "this game is kicking off in like two to three minutes". And he's reading this email and I'm thinking what is going on!"

Keane added: 'That would annoy me! But he does multitask and for all his roles, Salford, his hotels and Sky. To me one of them jobs is your only job.

'But he's got loads going on, whether he is missing something upstairs. He's lacking something obviously! I think there is a bit of madness to Gary. But part of me admires him for his multitasking.

SPORTbible and Sky Bet’s ‘Agree to Disagree’ is available on LADbible TV on YouTube.