The 18-year-old, who scored in the 1-1 draw at Bolton Wanderers, suffered the injury when he clashed studs with Bolton's Abdoulaye Meite and television pictures showed his boot covered in blood.
"James severed an artery, it was not a break but it was spurting out blood," manager David Moyes told the club's Web site (www.evertonfc.com)
"The doctor stitched him up but the foot has blown up again."
Moyes said the full extent of the injury would be known in the next 24 to 48 hours.
"I just hope we are not going to lose him because we cannot afford to lose any more players," Moyes, whose side are pushing for a UEFA Cup spot, added.