The Tottenham boss said it would take an 'amazing figure' - equivalent to the fee Real Madrid paid Manchester United for Cristiano Ronaldo in 2009 - for the 21-year-old to leave White Hart Lane this summer.?
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The pair will clash at the Bernabeu on Tuesday night after both were passed fit for the first leg of Madrid and Tottenham's Champions League quarter-final.
Redknapp insisted Spurs must hold on to their star players if they are to remain a club challenging for European honours.
He said: 'Once you start selling one, it sends out the wrong signals. 'Manchester United sold Ronaldo but they got an offer of ?80m so in the end it was good business. But we wouldn't want to sell a player like Gareth Bale at this time, when we're trying to build the club.
'It would have to be that type of figure. It would be an amazing figure if you ever sold him. But how do you replace a player like that? Once you start selling off your prized assets - I had it at West Ham.
How would you replace Gareth? Redknapp says he'd only accept an outrageous offer for his star man
'We let Rio Ferdinand and Frank Lampard go and then Joe Cole and the rest followed. 'If you are looking to build a club, you can't be selling Gareth as then Luka Modric wants to go and someone else wants to go. Then you end up where Tottenham were for four or five years, finishing half way up the table each season.'
Bale signed a four-and-a-half-year deal at Tottenham only 16 days ago, but has told Spanish newspaper AS he would consider playing abroad.
The Welshman said: 'You never know, but I'm not afraid to leave the country. 'If a great opportunity arises you need to seriously consider it. I left home at 15.
In training: Bale (right) and Gallas are put through their paces ahead of Tottenham's Euro clash
'If I leave the Premier League, I'll learn another language, I'll know other people, another country, I will grow as a person. 'There aren't more British players abroad because the league is very strong, but now the Spanish league has got Cristiano Ronaldo and Lionel Messi.'
Redknapp responded: 'The day that Gareth Bale comes in and says that he wants to go, or the agent says that he wants to move, there is very little you can do about it. But I don't see that happening. 'He signed a contract. And maybe he doesn't want to sound unambitious.
'If people ask him whether he wants to play for one of the top European clubs one day, I am sure that he would.'But I don't think that he is ready to do that. He needs a few years playing at home.'
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When asked about Real Madrid's interest in Bale, manager Jose Mourinho said: 'I think I was one of the first to say he will be an amazing player.
'I was saying that when he was not yet known in European football, just in England, so I know the great player he is.
'He is still young. He will be a really top, top, top player. I have no doubt about that.'
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?Explore more:People: Cristiano Ronaldo, Harry Redknapp, Luka Modric, Rio Ferdinand, Joe Cole, Gareth Bale, Frank Lampard, Jose Mourinho, Lionel Messi Places: Madrid, United Kingdom
Source: Daily Mail
Source: Daily Mail