Federico Macheda and Mame Biram Diouf should also start on Wednesday as manager rotates his squad to keep players fresh and give several youngsters a chance to impress
Sir Alex is set to make wholesale changes from the side held at home by Newcastle on Saturday, with Federico Macheda and Mame Biram Diouf also likely to start.
The United boss revealed he has not yet decided whether to play either Morrison or Pogba from the start against the Championship side, but confirmed both should at least make the bench for the match.
"There will be complete change. Just the same as we had at Leeds and Aldershot," Sir Alex said, according to the club's official website.
“Ravel Morrison was in the squad for Wednesday's game [against Benfica]. He's a very, very talented boy, of course, and he'll possibly be on the bench, at least, in midweek.
“But I've got other players needing a game like Mame Biram Diouf and Federico Macheda.
"All the younger players [will come in] - Zeki Fryers, the two Da Silvas [Rafael and Fabio] are possibles.
“Chris Smalling has come back and I may be able to play him on Wednesday. He's still young and it'll be a young squad against Palace.
“The only area where I've got problems is centre midfield. It's possible I could play Pogba in there but we'll wait and see. I've got enough players to choose from, that's for sure."
Sir Alex also revealed he believes the League Cup has become a useful tournament for big clubs to blood their young stars.
"I think the League Cup has turned into quite a good tournament," he added.
"Clubs like United are able to introduce young players and ones who have not been playing regularly in the first team and it's been good to us over the years.
"We've won two finals at Wembley with young players, which is good going, and I think it's become an important tournament for us in terms of getting the youngsters an introduction into winning and having an understanding of the progress they're making."
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