Both Spurs, long term admirers of the Ivory Coast forward, and Manchester City, are both keen on Zaha, who is rated at at least £25 million.
The Selhurst Park club, in a bid to keep their star player, are preparing to open talks over a new contract with the 24-year-old.
Zaha is on a £35,000-a-week deal which runs out in 2020 but the new offer will bring him in line with the top earners at the club on around £100,000.
Both Manchester City and Tottenham are chasing the signature of Wilfried Zaha
Wilfried Zaha has rediscovered his best form at Crystal Palace this season
Spurs manager Mauricio Pochettino is a big admirer of the winger, and his club will come back in this summer after having a £12m offer rejected last year, described by Palace chairman Steve Parish at the time as “ridiculous”.
But Allardyce, speaking at the Crystal Palace Foundation’s relaunch as the Palace for Life Foundation, said: “Wilf, us and the clubs that want him will decide his future in the end. There is always a point where it may be impossible to turn down what is offered. That is realistic.
“Hopefully, we do not get to that point for a long time but it may be a possibility. Because he is a rare talent.
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Mauricio Pochettino is a big admirer of the winger
“Who knows how much he is worth? The Premier League has got bigger competition than ever before. It is called China.
"Now the Chinese are looking at the younger ones, and are paying bigger money than the Premier League has ever paid out to entice them to go to China.”
Parish said: “We will sit down at the end of the season and I am very confident we can keep Wilf.
"We are looking to improve the squad, and he is an intrinsic part of what we are doing.”