Manchester City midfielder Bernardo Silva appeared to suffer a muscle injury on international duty just days before the start of the Premier League season.
Silva started for Portugal in their Nations League meeting with Sweden on Tuesday but lasted just 22 minutes.
The City man was injured while sending in a superb right-wing cross for Pepe, who could not turn the ball goalwards.
Silva indicated an issue in his leg as he received treatment on the pitch and was quickly replaced by Goncalo Guedes.
The new Premier League campaign begins on Saturday, although City are not involved until September 21 at Wolves due to the short turnaround since last season's Champions League.
Pep Guardiola's right-sided options have already been hit as Riyad Mahrez tested positive for coronavirus, while Phil Foden missed England's match in Denmark after breaching protocol relating to COVID-19.