Carlos Cuellar has revealed that Stiliyan Petrov's acute leukaemia was discovered after the Aston Villa players underwent medical tests in the wake of Fabrice Muamba's collapse.
The football world has again come together over the past few days to show support for Petrov, just a couple of weeks after Bolton midfielder Muamba suffered a cardiac arrest during a match against Tottenham.
Muamba was taken to the London Chest Hospital and has made encouraging progress in his recovery, but what happened to him at White Hart Lane brought the issue of heart screening into the spotlight and a number of Premier League clubs decided to check over their squads.
And it emerged last week that Petrov had been diagnosed with leukaemia after developing a fever following the defeat by Arsenal.
"Last Tuesday, after what happened to Muamba, experts came to our training ground to do tests on us and examine our hearts," Villa defender Cuellar said in The Sun.
"Two days later, we received the results and they communicated to Stan his symptoms of cancer.
"They wanted him to go to hospital for more tests to confirm the original diagnosis.
"At the beginning they didn't even tell him the truth directly and he didn't want to scare us either, with a game against Chelsea so close on Saturday.
"They had told him 'Yes it could be cancer but we need to do more tests'.
"So he didn't tell anyone but it's true his closest friends knew there was this possibility that it could be cancer."
Petrov, 32, only told the whole of the Villa team once the news was confirmed on Friday, and Cuellar admits it has been difficult to come to terms with.
In an interview with Spanish radio station COPE, Cuellar added: "The truth is we are very much affected by the very bad news about our captain.
"No one expected it, it caught us by surprise and left us in shock.
"Last week we were still affected by the situation of Fabrice Muamba - it affected us mentally and psychologically.
"So imagine if it is one of your intimate friends, a comrade with whom you've shared a dressing room for four years.
"My team-mates and I are deeply affected and very emotional but Stiliyan is the first to give us strength, trying to lift us so that we win as many games and points as we can.
"It's the only thing he asked of us."
Petrov started his treatment on Monday and Cuellar believes he can beat leukaemia, especially with the support of his family and team-mates.
"He knows it's a tough situation but he's certain he will win - and his family is giving him strength," said Cuellar.
"His first priority is to keep his wife and kids happy and recover as quickly as possible for them.
"He's a strong guy and he will definitely pull through.
"He's also a courageous man and knows he can give courage to many other people who are suffering the same fate."