Kobbie Mainoo makes England's starting 11 against Slovakia

"He has played some huge games already for his club," Southgate told ITV's Gabriel Clarke about his decision to start the teenager. "He looks at ease in our environment."

After making the decision to start defender Trent Alexander-Arnold at midfielder for the first and second games, Southgate opted for Conor Gallagher in the Group C finale.

On Sunday, Southgate admitted to Clarke that Mainoo's ability to use the ball will help England get "through their high pressure" against Slovakia.

The Manchester United academy graduate will become England's third-youngest starter (19 years, 72 days) in a major tournament behind only Michael Owen (18 years, 198 days) and Wayne Rooney (18 years, 244 days).

Figuring out who to pair in central midfield alongside Declan Rice has been Southgate's only headache since the rest of the squad has gone unchanged.

Switzerland, a 2-0 winner against Italy, awaits the winner between Slovakia and England for a meeting in the quarterfinal on Saturday.