The boss revealed that he will also hopes to rest Ruben Dias and Joao Cancelo on Tuesday evening, with three huge games to come the week after.
“Rodri had some muscular problems - not big, but I don’t know how many days. The doctor could not tell me,” said Pep.
“And my captain (Fernandinho) is my captain. He tried and he did it and like all of us we were not precise and not clear in our actions. All of us we struggled against Southampton.
“I don’t have any alternative (but to play youngsters). We are going to play a few young players.
“Some players might rest for the games we have coming up ahead of us and yeah a few players from the Academy are going to play.
“We have John, Aymeric, Oleks, Rodri - I think Gundo - all of them injured.
“Ruben played all of the minutes so far and Joao played all of the minutes, too, so I don’t think they will be able to play in this game.
“We will see after Sunday to make a good selection. It's a good opportunity for the Academy - that’s why they are there.”
The boss also said he wanted to see his players press better than they did against Southampton, adding work on the training ground was the only solution.
“Practice,” he said. “Practice and convince them that this is the way we have done it for many years and it’s good to do it.
“When something is not good in our pressing and the way we play we have to practice.”