Real Madrid is expected to sue Eufemiano Fuentes after the doctor, the centre of the Operation Puerto doping saga, appeared to suggest he previously had links to medical staff at the club.
Operation Puerto emerged in 2006 when frozen bags of blood and plasma were seized from a clinic run by Fuentes in Madrid following a police raid.
insidethegames revealed in 2019 that the implicated athletes cannot be named due to the 10-year statute of limitations having ended, despite the World Anti-Doping Agency having identified 11.
Cyclists have been largely linked with the scandal, with Spain’s Alejandro Valverde, Tour de France winner Jan Ullrich of Germany and Italy's Ivan Basso among few to have been outed.
Athletes from other sports were also allegedly involved, including athletics, football and tennis.
Fuentes was asked by journalist Jordi Evole about his alleged links to Spanish football clubs Barcelona, Real Madrid, Real Sociedad and Valencia during the Lo de Évole programme.
Fuentes denied having any relationship with Valencia and said there had been contact with Barcelona on two occasions but no agreement was reached.
When asked about Real Madrid, Fuentes pauses before saying: "I'm not going to answer that question."
La Sexta journalist Josep Pedrerol has reported that Real Madrid plans to take legal action against Fuentes following the answer.
Barcelona 1992 Olympic men’s 1500m champion Fermín Cacho is also reportedly considering legal action.
Fuentes named Cacho as one of 15 Spanish athletes he had worked with prior to the Olympic Games.
"If I told everything I know, it would be very harmful for Spanish sport. But I cannot tell it for professional coherence. I think that some Spanish medallists at the Barcelona Games took drugs, I believe it, but I cannot prove it," Fuentes said, according to Spanish newspaper Marca.
"I was a doctor of the same fifteen athletes.
"The Olympics are prepared in cycles, four years ahead, and the services are paid by the athletes.
"I saw Fermín in a cafeteria and the other in the stands.
"They asked me for privacy.
"My satisfaction was to do my job well and get paid for it, but I am not going to give a series of names that I did not give fifteen years ago when I was arrested."
When asked specifically about Cacho, Fuentes claimed he had been given "plasma expanders, lactic acid reducers, natural stimulators of the hormones testosterone or amino acid."
The substances were not banned at the time, but would be classed as doping under current rules.
Cacho has reportedly said he will make a decision "sooner or later" on whether to take legal action against Fuentes.
The Olympic champion has suggested he could sue due to Fuentes violating his patient confidentiality, while expressing his innocence to the claims made by the doctor.
Fuentes was sanctioned during the original Operation Puerto case with a one-year suspended sentence.
The sentence was given on public health grounds, as doping was not considered a criminal offence in Spain at the time.