Geraghty, 20, suffered a recurrence of the same hamstring strain which forced him to miss the closing weeks of the Guinness Premiership season.
That has fuelled fears he could be set for another prolonged spell on the sidelines, potentially ruling him out of the Saxons' remaining Churchill Cup matches and thus preventing him from staking a claim in Brian Ashton's senior squad.
"It's so frustrating," said Geraghty, who undergoes a scan on his right hamstring on Saturday.
"It's the same injury and the same hamstring.
"It's too early to tell if I'll be out for the rest of the tournament but it doesn't feel too great at the moment."
He confirmed his rich potential in March with a stunning debut performance in the RBS 6 Nations victory against France at Twickenham.
His sublime run and underarm offload which sent Mike Tindall scampering over the line for an try that will live long in the memory.
But, having initially sustained his hamstring injury against Saracens on March 23, Ashton decided against taking him to South Africa for the Tests in Bloemfontein and Pretoria.
Geraghty was told to use the Churchill Cup as a stepping stone to the World Cup.
"Brian said it would be better to be involved in the Churchill Cup and play some games, but then I've gone and got injured again," sighed Geraghty.
"It's pretty annoying but it's one of those things.
"This was meant to be about me making my comeback and then getting a few games under my belt.
"Now, I've got to try and work hard and get back in contention for the World Cup or even the Churchill games coming up, in order to give me a chance.
"Fingers crossed the injury won't be as bad as last time."