The England youth international has been linked with a host of Premier League clubs in recent days, including Liverpool, Manchester City and Tottenham Hotspur.
Despite the speculation, Parish has warned any interested parties that his club are not prepared to part with the 19-year-old cheaply.
"[Zaha] is an extraordinary talent," he told the South London Press. "I said at the start of the season that keeping hold of Wilf would be like spending a lot of money on a transfer.
"Other sides can fly their kites but it would take £20m before we even got interested.
"He has got the lot, provided he keeps his feet on the ground and continues working so hard on his game - then it will all come."
Zaha has scored four league goals for the Eagles this season.