The Well were drawn against Aberdeen in the quarter-finals on Thursday and will now look to win their first piece of silverware since the 1991 Scottish Cup by breaking a League Cup drought which dates back to 1951.
"I have grown up saying you want to win every competition that you enter. But you have to be realistic as well, Celtic are going to run away with the league," he told Press Association Sport.
"If you can win a cup here, it would be a massive achievement. The last time they won one was '91. So that would be brilliant."
As for their hopes away from the cup, McManus suggested that Motherwell could perhaps be the second best team in Scotland.
"It's going to be a tough season but we certainly feel we are as good as anyone in the league outwith Celtic."