The Nigerian striker, who scored 15 goals last term, injured his ankle in a recent pre-season friendly against Bristol City and may miss Sunday's home clash with reigning champions Manchester United according to manager Roy Hodgson.
"Peter has a sore ankle, which came about after the Bristol City game. We were hoping it would recover in time for yesterday's game but it didn't," he said.
"Now we're hoping it won't go beyond next week. Ankle injuries can take time. You can't play without ankles and knees! I wouldn't want to put a timescale on it.
"All I want to say is the medical staff are very optimistic he'll recover, so I've got to be optimistic.
"There was no chance of risking him yesterday, but I'm sure he'll be desperate to play against United and we'll be happy to put him in the team if he's fit.
"We'll be monitoring it during the course of the week. The same goes with Steven and Jerome Thomas.
"I'm a little bit more optimistic about those two."