Callum Hudson-Odoi will make his first England start against Montenegro on Monday night.
Chelsea winger Hudson-Odoi, 18, became England's youngest competitive debutant in Friday's 5-0 win over Czech Republic, eclipsing Duncan Edwards' record set in 1955, and is now set to make his full debut in Podgorica.
Jadon Sancho, also 18, is expected to miss Monday's Group A European Qualifier with an unspecified injury after making his first competitive start for England in Friday's match at Wembley.
England manager Southgate said on Sunday night that Sancho, Jordan Henderson and Dele Alli all face late fitness tests to decide whether they will play in Podgorica.
Southgate also said that he would have no reservations in putting the youngsters into a potentially hostile atmosphere inside the Gradski Stadium.
The England manager considered calling up reinforcements from the U21s but opted against it to avoid disrupting Aidy Boothroyd's preparations for a key game against Germany, despite potentially only having 17 outfield players available.
Southgate's options have been drastically reduced by injury with Luke Shaw, Ruben Loftus-Cheek, Marcus Rashford, Trent Alexander-Arnold John Stones and Fabian Delph all withdrawing from the squad.