Barcelona cancelled meetings with the club president and journalists on Wednesday amid reports that coach Tito Vilanova is ill.
The club said on its website "it has suspended a meeting with President Sandro Rosell scheduled for this afternoon" and "cancelled Christmas lunch with the media."
Barcelona said that a new statement would be released later in the day.
The 44-year-old coach had a tumour removed from a saliva gland in November 2011. He took over as Barcelona's team coach from Pep Guardiola this season after passing medical checks and with the approval of the doctors who had treated him.
Sports newspaper Mundo Deportivo said on its website that Vilanova had fallen ill and leading newspaper El Pais reported he has suffered a relapse of the cancer, citing unnamed club sources.
Marca sports radio said Wednesday afternoon that the club had not yet had an opportunity to break the news officially to its players, but most of Spain's media was buzzing with headlines about Vilanova.
"Very sorry to hear the news," Barcelona midfielder Xavi Hernandez said on his official Twitter account.
'All my strength and support'
Jordi Roura, Vilanova's assistant coach and a former Barcelona player, was being mentioned by El Pais as the person most likely to take over.
"All my strength and support to Tito Vilanova," Spanish tennis star Rafael Nadal said on his Twitter account. "We are all with you so you may overcome this news step."
Under Vilanova's guidance, Barcelona has made its best ever start to a season, winning a Spanish record of 15 of its first 16 league games.
The club leads the standings with 46 points — nine ahead of Atletico Madrid and 13 in front of archrival Real Madrid.
The club's charge has been led by Argentina forward Lionel Messi, the three-time FIFA world player of the year. He has scored 90 goals in 2012, surpassing Gerd Mueller's 40-year-old milestone of 85 in a calendar year.