According to a Spanish national radio, surgeons at Hospital Quiron in Barcelona carried out an operation on the 45-year-old Vilanova to alleviate gastric problems.
The radio station said Vilanova, who has asked the media to respect his privacy during his treatment, had been admitted to hospital April 18.
However, it was gathered that when contacted, Hospital Quiron declined to say whether Vilanova had been admitted, citing medical privacy.
As at the time of filing this report, Spanish football club Barcelona has not made any official statement concerning the report.
"The club does not comment on this matter," a spokesman for Barcelona said.
* Ex-Barcelona coach, Tito Vilanova is reported to be in critical condition in a hospital in Spain
Messages of support have flooded social media network Twitter since the news broke out Thursday night.
Goalkeeper Valdes, who has announced his intention to leave the club at the end of the current campaign, appeared to be the only member of the team to make any public comment.
"Stay strong boss!" injured Barcelona keeper Victor Valdes said in a message.
Vilanova was diagnosed with cancer of the salivary gland more than two years ago and was forced to step down as Barca boss last July.
He was Pep Guardiola's assistant during a glorious four-year spell for Barcelona between 2008 and 2012 during which the club won 14 trophies.
Vilanova took over from Guardiola at the start of the 2012/13 season. He was forced to take four months off between December 2012 and April 2013 for treatment in the United States after a recurrence of the throat cancer which had been first diagnosed in November 2011.
Barca went onto win the Spanish La Liga title, equalling the record points tally, in his only season in charge before he finally resigned because of the cancer.
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