The 44-year-old coach may have to undergo cancer treatment and if that happens then the club may have to look for at least a temporary replacement
The 44-year-old, who took over from Pep Guardiola earlier this year, underwent emergency surgery in November 2011 on his parotid gland, and widescale reports from Spain say his tumor has become malignant again.
Vilanova has guided the Blaugrana to the best-ever start in La Liga, which has seen them go unbeaten for 16 games, and sit atop of the table with 46 points, holding a 13-point lead over arch-rivals Real Madrid.
News of his health problems come only one day after defender Eric Abidal got the green light to make his comeback, after spending the majority of 2012 on the sidelines due to a liver transplant.
Barca have yet to comment on the matter, but cancelled a Christmas lunch with the media, and are expected to release an official statement later on Wednesday.
The club have also confirmed that Wednesday's training session will not be open to the press.
Further reports suggest that the Catalan giants have denied contact with Pep Guardiola and Luis Enrique about the possibility of replacing Vilanova.
It is understood that Vilanova will undergo surgery on Thursday morning.