Vidic has shaken off a calf complaint and returned to action for Serbia in midweek.
“The big question mark is whether Vidic is ready,” Ferguson said.
“He has his first game for Serbia on Tuesday. It’s certainly a consideration because he’s such a great competitor.
“He came in yesterday (Thursday) and felt OK. But the Liverpool game is such an intense, stamina-draining game that you want everyone to be 100 per cent so it might be more down to how he feels himself.
“Jonny Evans’ form has been absolutely brilliant so I don’t have any real concerns about who I play because they’re all playing particularly well.”
