England captain Leah Williamson has been ruled out of the games against USA and Czech Republic after sustaining an injury in training.
Earlier on Tuesday, the Football Association said Williamson had picked up the unspecified issue in training and was to undergo further assessment, but the defender has now returned to Arsenal for further assessment.
Williamson left the England camp in a protective boot and on crutches.
Sky Sports' Anton Toloui said: "Williamson picked up an injury in training on Monday.
"She was assessed on Tuesday afternoon and the FA is giving no details about the type of injury or the severity of the injury, but I do know Williamson left today in a protective boot on her right foot and on crutches."
While the news is a big blow for England, it will be a big concern for Arsenal, who get their Champions League campaign under way against defending champions Lyon in two weeks' time.
Wubben-Moy and Parris called up
Fellow defender Lucy Parker, who had been called up for the first time, has returned to West Ham to continue her rehabilitation after being injured in Sunday's League Cup match at London City Lionesses.
Lotte Wubben-Moy, another Arsenal defender, and Manchester United forward Nikita Parris have been added to the squad.
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Russo also absent for England
The news of Williamson's injury comes a day on from Manchester United striker Alessia Russo pulling out due to injury.
Friday's Wembley clash between Sarina Wiegman's European champions and World Cup holders the USA is a sell-out.
England will then play the Czech Republic at the Amex Stadium next Tuesday as the build-up to next summer's World Cup in Australia and New Zealand continues.
'A big blow for England, but also Arsenal'
Sky Sports News' Anton Toloui:
"It's big breaking news for England but it is big breaking news for Arsenal as well.
"It is big news for England, obviously, because they want their captain and their first choice centre-back going into that huge game against the world champions, the USA on Friday.
"But also, Arsenal kick off their Champions League campaign against champions Lyon in France in two weeks' time."
'We'll miss Williamson but England squad depth good'
England forward Chloe Kelly:
"Leah's a great leader and of course we'll miss her.
"We have such great depth in our squad and so much strength in our squad.
"There are so many great players with experience so it's all about coming together in these moments where you do lose a player like Leah, and supporting Leah in her rehab.
"We all get behind each other and on the pitch we look after each other too.
"The strength in our squad is very good and that really helped us in the summer.
"The bench was unbelievable. We enjoyed the moment and got behind the girls, and we were ready for our moment as well.
"It's the same again this week and be ready for your moment."