The Argentine has had some dodgy moments in his first season in the top flight.
The Southampton boss said: "We know he can make saves.
"It's the other aspects of a young goalkeeper's development - the decision-making process - that you go through when you're young.
"He's only 20 and, like all our players, he will get the opportunity to go out there and he will make saves but he will also make some mistakes.
"You're only going to get better by being in the situations where you have to make those decisions."