The French defender, 20, picked up the injury in Tuesday night's Worthington Cup defeat by Grimsby Town and left Anfield on crutches.
"I've had an x-ray and I have fractured my foot in two places," Vignal told the club's official website.
"It is a bit uncomfortable but I don't think I will will be out for too long.
"Hopefully it will just be a couple of weeks out of action. I hope it is no longer than that because I feel as though I am doing well in the first team at the moment and I don't want to be spending time in the treatment room."
The talented defender is definitely out for the Premiership clash with Leeds on Saturday morning and gives manager Gerard Houllier a further selection headache ahead of the Anfield encounter.
Stephane Henchoz is sidelined with an Achilles problem and Markus Babbel is still recovering from a virus infection.
Houllier could be forced to play Jamie Carragher alongside Sami Hyypia and move John Arne Riise and Stephen Wright in to the full back slots.
