The 29-year-old, who scored 17 goals and provided 14 assists in 54 appearances in all competitions for Aston Villa in the recently concluded season, has been capped 18 times for England, netting five times.
With Watkins' withdrawal, captain Harry Kane and Ivan Toney remain England manager Thomas Tuchel's striker options for their two upcoming games.
England play Andorra in a 2026 World Cup qualifier in Spain on Saturday before hosting Senegal for a friendly match on Tuesday.
