The Brazilian spent last term on-loan with Granada.
Robson told manutd.com: "I haven't see too much of Andreas Pereira since he went abroad [to Granada] but he had great ability and hopefully a year's loan will have just brought him on and made him a better player.
"It will be interesting to see how he does when he returns and I think we've got quite a few good young players who, next season, have got to step up a little bit more and prove they can be Premier League players week in and week out.
"They've always got to remember it's not just a one-off game but they have got to come in and handle it - mentally and physically every week. When they've been around the first-team squad for a couple of years and keep doing it, then that's the time to say they've really arrived at Manchester United.
"There is still a lot of hard work to be done for those kids."