Evra was replaced by John O'Shea at half-time of their 5-1 win at Newcastle, while Vidic limped off during the second half, seemingly still feeling the effects of an earlier challenge by Michael Owen.
Ferguson told MUTV: "Patrice wasn't feeling very well. He was sick at half-time so we took him off.
"Then Vida came off. I think he's okay - hopefully it's just a calf strain."
Following the midweek Champions League draw at Lyon, Ferguson made four changes against the Magpies, leaving Ryan Giggs out of his squad entirely.
"Ryan got a kick below the knee on Wednesday," the Reds boss added. "I wasn't going to start him after his exertions against Lyon."