Chelsea have suffered yet another setback in the early stages of the new season after Essugo, 20, picked up a knock during the September international break.
Levi Colwill is expected to miss most of, if not all, of the 2025-26 campaign after rupturing his ACL during pre-season, while Liam Delap and Cole Palmer have also picked up injuries.
Essugo has now withdrawn from the Portugal under-21s and will return to Chelsea as they assess the severity of his issue.
“The Chelsea midfielder was excused from training due to a muscle problem in his right thigh, which he suffered after training on Monday,” the Portuguese Football Federation confirmed.
“The athlete was evaluated by the Portuguese Football Federation’s Health and Performance Department on Tuesday morning and was declared unavailable.”