The Ecuador international was taken off 12 minutes from the end of last Saturday's 1-1 draw with Stoke City after picking up a foot injury.
Valencia had only just returned following a lengthy lay-off but fears have been eased after he completed an individual training session on Wednesday.
Head of medical and sports science, Stijn Vandenbroucke, told West Ham's official website: "We are firstly pleased to confirm that Enner Valencia completed an individual training session on Wednesday morning, after suffering a foot injury in Saturday's draw with Stoke City.
"Enner has a good chance of being available for selection for the trip to Manchester City on Sunday.
"Diafra Sakho, Andy Carroll, James Tomkins and Doneil Henry are all continuing with their rehabilitation as planned and are progressing as we would expect at this stage."
