A club spokeswoman confirmed on Sunday afternoon that the Portuguese winger suffered a "very deep gash" in his ft leg after Carragher's challenge shortly before half-time.
The Liverpool defender was booked by referee Phil Dowd and Nani played no further part in the match. He was carried off the field on a stretcher and replaced by substitute Javier Hernandez who later scored United's only goal with a header in injury time.
While fans will naturally be worried about Nani - one of United's best players of the season so far - there was some encouraging news in that his fellow winger Antonio Valencia was part of the Reds' travelling party for the Liverpool game.
The Ecuadorian was not named among the seven substitutes by Sir Alex Ferguson but his presence at Anfield, combined with his recent return to full-contact training, suggests a comeback may be close.