Telecommunications magnate Ambani, 49, has more money than Roman Abramovich after amassing a £21billion fortune and is competing with Singapore-based investors Profitable Group for the Tyneside club.
He is desperate to break into English football and will turn his attentions to Leeds United if his offer is turned down.
A source close to the deal said last night: "Ambani's people have seen how Ashley dealt with the last round of takeover revelations and will not stand for any nonsense. Ambani means business and if Newcastle drag their heels he will be off to invest somewhere else and show Ashley just what he is missing out on."