The Albion striker pulled up with the problem after an innocuous incident in the final seconds of training last Sunday and has missed subsequent games against Watford and Sheffield United.
And now the United States international frontman faces a race against time to recover for the World Cup - in which his nation face England - which begins in November.
It is a separate injury to the torn hamstring that ruled the £7million signing out from January to the end of last season.
Steve Bruce, whose side secured progression to round two of the Carabao Cup after beating the Blades 1-0, is chasing forward replacements in the transfer window given the hammerblow to Dike.
There is also concern after Karlan Grant, the first round match-winner, hobbled off with a sore back after a heavy landing late on.
Bruce said: "The scan results have confirmed our fears that he's got a tear to his thigh muscle. Last time it was his hamstring. We're devastated for him and for the whole lot of us. I don't want to put a timescale on it, because that'd be unfair.
"It's substantial, it'll be weeks, at least a couple of months. He's got to stay mentally strong the kid, because he's had an awful time and the way he's worked and the way he got himself into the condition he's in, it's really disappointing for him and everybody.
"He's kicked a ball. It's so innocuous that it's scary. He's tried to score a goal. It might even have been just a tap in, last minute of training session. It's frustrating for everybody."
Bruce, meanwhile, confirmed Villa striker Keinan Davis - who spent the second half of last season on loan at promotion-winners Nottingham Forest - 'is an option'.