The Daily Star says Tottenham are now regretting not trying to sign Grealish earlier in the transfer window.
Spurs were not prepared to increase their £25m valuation on the midfielder, 22, when Aston Villa were demanding £40m.
But as Spurs remained convinced the deal would go through before last Thursday's transfer deadline for Premier League signings, the game changer was Villa's sudden ownership change.
Villa's new regime not only rejected Tottenham's eventual offer of £25m but also insisted Grealish was not for sale.
The midfielder had his heart set on a move to Mauricio Pochettino's squad but Villa are more interested now in negotiating a new deal.