The forward came off for a second successive game due to a hamstring problem.
Now the club is sending him for a scan to figure out the extent of the issue.
The Daily Mail suggests the club may have to take it easy with Antonio to ensure it does not become a more serious injury.
The 30-year-old came off during their 1-1 draw with Manchester City at the weekend, in which he scored.
Losing him for a run of games would be a huge blow to the Hammers, as Antonio is their top scorer this season.