The former Arsenal captain has struggled for fitness so far this season, only recently returning to first-team action in Inter's 2-1 victories against Milan and Bologna.
And although the Frenchman concedes he is not yet fully match-fit following his lengthy layoff, he is still disappointed not to be able to go head-to-head with former arch-rivals United again.
"I have not been picked," he told L'Equipe. "I am not injured, it is the coach's choice.
"Am I surprised? Yes, of course. I have been picked for the last two matches, so I thought I would be in this time, but the coach makes his decision.
"It is a big disappointment, but I know where I have come from and the trouble I experienced. I have been out for two-and-a-half months and I have trained fully for just a fortnight. I may be too short to play 90 minutes, particularly in such an important match.
"I have nothing to do except to carry on working."
Inter, nine points clear at the top of Serie A, meet United, seven ahead in England, in a clash of the European titans at the San Siro, with Vieira stating the pressure is on the reigning European champions to triumph.
And with Ferguson's side currently suffering a defensive crisis, with Gary Neville, John O'Shea, Rafael and Jonny Evans struggling and Nemanja Vidic suspended, the 32-year-old says Mourinho's men have nothing to fear.
"Considering their European past, and the fact they are the title holders, Man United are the favourites," he said.
"They have been dominating English football for a few years. It is a stable group, very united. They have fun playing together, you can see it. But, considering the starting XI, we have nothing to be jealous of."
