George Boateng has been relieved of the Middlesbrough captaincy to concentrate on his football.
Gareth Southgate told the Evening Gazette: "I made the decision because I wanted George to be able to concentrate on his game.
"Julio has already proved himself to be a good leader and I felt it would be of benefit to everybody.
"George's performances have been excellent and I want it to stay that way. I want him to be free in his mind to enjoy his football.
"I've explained the situation to George and he is totally at ease with the situation.
"His professionalism has been excellent over the last couple of weeks. His performances show how much pride he has in his personal contribution."