This story has been reproduced from today's media. It does not necessarily represent the position of Liverpool Football Club.
By Jamie Carragher
They are the best players in the world but they will never be best friends. When Cristiano Ronaldo and Lionel Messi go head-to-head on Tuesday night, there will be a brief acknowledgement but nothing else.
Really, though, they should go out of their way to thank each other. Every time Ronaldo sparkles for Real Madrid, Messi inevitably tries to go one better for Barcelona.
The results have been spectacular and it means Spanish football is now essential viewing.
But watch them in the second leg of the Copa Del Rey semi-final - and again on Saturday in la Liga - and you will see nothing more than a cursory handshake. You don't need to be a body language expert to appreciate there is no love lost between these two.
The question both men should be asking, however, is this: where would I be without you?
You have to question whether their statistics would be so incredible if one was playing in another league. When Ronaldo scored a hat-trick last month against Getafe, Messi scored four the night after against Osasuna.
All that was missing from his performance was him lifting his shirt to reveal the message 'anything you can do, I can do better.'
Messi has always been a top player and is surrounded by magicians in Xavi and Andres Iniesta but you can argue that Ronaldo's £80million move from Manchester United in 2009 took his game to another level.
Statistics back that up. If you look at a breakdown of how Messi has reached 300 goals, the first 80 came in 161 games. In the 204 matches he has played since Ronaldo arrived at the Bernabeu, Messi has rattled in 221, as if to hammer home the point he is the best in the world.
Ronaldo, of course, would never acknowledge that nor would he say that trying to outwit Messi has taken his game to another level - he scored 118 goals for Manchester United in 292 appearances but, for Madrid, his tally is 183 goals in 182 matches.
His enmity towards Messi really surfaced last summer at Euro 2012, when Denmark fans barracked him during a game against Portugal, chanting 'Messi!' every time he got possession.
'You know where he was this time last year,' Ronaldo asked after the game. 'Being eliminated from the Copa America. In his own country. That is worse, no?'
Further proof arrived via the voting for the Ballon D'Or, which Messi won for a fourth time recently. As captain of Argentina, Messi was given a vote and his top three choices were Iniesta, Xavi and Atletico Madrid's Radamel Falcao.
Ronaldo, meanwhile, also got the chance to vote, as he is captain of Portugal. Yet he turned down the chance and handed responsibility to his deputy Bruno Alves. Unsurprisingly, Alves picked Ronaldo as his number one and left Messi off his shortlist.
Of course, rivalry in sport is nothing new. Look at Sebastian Coe and Steve Ovett. Would Coe have won the 1500metres gold medal in Moscow in 1980, had he not been beaten six days earlier by Ovett in the 800metres?
The intense competition between those two was the reason there was a golden age for British athletics in the 1980s and I read that Coe cited his rivalry with Ovett as the reason he broke three world records in the space of 41 days in 1980.
Similarly, there was no affection between Ayrton Senna and Alain Prost when they dominated Formula One. Would they have enjoyed so many podium finishes without the other pursuing them?
Senna, after all, was known as a risk taker because Prost kept pushing him.The tragic footnote to that rivalry came when Senna was killed in 1994 and Prost said that 'part of him also died' with Senna.
They had no allegiance on the track but the respect Prost had for Senna was shown when he was one of the pallbearers at his funeral.
It is all about appreciation and recognition. Victoria Pendleton and Anna Mears, the top women cyclists, had a feud that lasted years but melted in a second when they embraced at the end of a sprint, which Mears won, at the Olympics last summer.
That was two athletes realising the role they had played in each other's career, a fitting way to bring the curtain down on their rivalry.
Will that happen with Ronaldo and Messi? Unlikely. Ronaldo was pictured with a face like thunder when Messi was presented with the Ballon D'Or. Messi, on the other hand, has not once said in public how good Ronaldo is.
They emit mutual loathing rather than mutual respect.Should that stay the same way, it would be a huge shame. Both men have fantastic team-mates and have enjoyed the backing of brilliant managers but they should also appreciate their private competition is making them play better, possibly better than they could ever have dreamed.
So while they might not be able to live with each other one thing is certain - they cannot be without each other, either.