Paul Parker: Immature hothead Sergio Ramos would be a £30m gamble

I've been seeing a lot about Sergio Ramos potentially moving to Manchester United, including Jamie Carragher saying how he'll transform United's defence if the move happens.

And the only conclusion I can come to is that Jamie is saying it because he's delighted at how Ramos's string of red cards would help out Liverpool.

The bottom line is that Ramos is just not mature enough. And given that he's already 29, he probably never will be.

What United need is a calm, experienced figure at the heart of the defence - not a hothead who badgers the referee every time a decision goes against him. His insistence on getting involved all the time shows that he's not concentrating fully on what he needs to do.

And it's not just his temper flare-ups, either. You could see his rashness in the Champions League semi-final against Juventus - charging around, getting out of position, giving the ball away, and giving away the free kick which led to the critical goal in the second leg.

Don't get me wrong, I watch him in the Spanish league and a lot of the time he's a good centre-half, with a great physical side to his game.

But what he isn't is the new Nemanja Vidic - and that's what United need.

So to spend £30 million on Ramos, at the age of 29? It's not for me to tell Louis van Gaal what to do, he's got far more experience than me.

But if I were him I'd be VERY careful. Ramos is a hugely expensive gamble.

He might work out, but there's a lot of things to suggest that he'd find it hard to adapt and get exposed in the Premier League - and given his age, he's going to have next to no sell-on value if things don't work out.

I actually think United would be better off going for Raphael Varane if they want a defender from Madrid, but the club don't seem inclined to sell the young Frenchman, where Ramos is actively seeking to force an exit.

That in itself is distasteful - I just can't get my head round how modern footballers get away with trying to dictate what they want. He signed his existing contract, he was happy to do so at the time, so why should he suddenly demand more money?

And that's what it boils down to for Ramos: money.

Ironically, the man who might be going in the other direction isn't concerned about money at all. For David de Gea, it's all about a triumphant homecoming.

And who can blame him for wanting to go to Real Madrid? He's been to England and tasted life here, proven himself among the very best in the world. Now, one of the biggest clubs in the world are offering him a dream chance to return to his hometown.

De Gea knows that these chances very often don't come around twice - if Real don't get him, they will get someone else who could end up being their goalkeeper for a decade.

So no wonder he is pushing hard to get the deal done - and that's exactly why United should sell him.

I played alongside guys who weren't happy and wanted to leave, but they were always English and looking for something new, not young guys thousands of miles away from friends and family.

De Gea won't want consciously take his foot off the gas if he ends up staying at Old Trafford, but now that the door is ajar it'll be painful for him if it gets slammed in his face. Instead of being raring to go for a new season he'll be there thinking what might have been - and if those thoughts get into his head, United will end up wishing they'd sold up while the going was good.