England have brought Leicester defender Ben Chilwell into the squad for the Nations League double header after Luke Shaw withdrew because of injury.
Foxes left-back Chilwell, 21, made his England debut as a substitute against Switzerland on 11 September.
On Sunday, uncapped Brighton defender Lewis Dunk, 26, was drafted in after an injury to Burnley’s James Tarkowski.
England face their World Cup semi-final opponents Croatia away behind closed doors on Friday and Spain on Monday.
Chilwell made his Leicester debut in October 2015 and after a loan spell as Huddersfield in 2015-16 has established himself as the regular left-back at King Power Stadium.
Shaw, 23, who was carried off with a head injury on England duty against Spain on 8 September, completed the whole match on Saturday as Manchester United fought back to beat Newcastle 3-2 in the Premier League, but complained of injury problems afterwards.
Dunk’s maiden call-up comes a week after the 26-year-old signed a new five-year deal with the Seagulls.
Tarkowski, 25, was forced out with a groin injury.
“He’s improved with every season, and on the back of an impressive first season in the Premier League he continues to progress,” said Brighton manager Chris Hughton said of his home-grown defender.
“I’m delighted he has now been given recognition at international level.”
Dunk will join fellow new recruits Jadon Sancho, Mason Mount and James Maddison at St George’s Park this week as Southgate rewards the centre-back for a fine start to the season.