Jones was selected by Roy Hodgson to be a member of the squad which took part in last summer's Euro 2012, and could be in action again this summer if selected for the Under-21 European Championships this year.
The 71-year-old United manager is surprised Jones will take part in Tuesday's game against Walsall for Stuart Pearce.
"I haven't paid much attention to it but I'm surprised he's in the Under-21s and not the full squad," Sir Alex told The Guardian.
"It's happened quite a few times to players [to drop down into the Under-21s] and it's understandable. But for the players that's more difficult to manage because once a player gets into a full squad he thinks he's achieved what he wants to achieve and taking the step back can be hard to manage. But he's 20 and maybe he's as good as the Under-21 squad are going to get."The prospect of Jones playing another summer tournament is not one that pleases Sir Alex either, especially given the player's problems with a knee injury this season.
"We'll have to wait and see how things are," he added. "The boy's had an injury this season, which has needed looking after. We'll see what it's like in the summer."