Petrov’s illness was discovered in medical tests carried out on the 32-year-old Bulgarian international after he came down with a fever following last Saturday’s defeat at Arsenal, the club said.
“We expect to learn more about Stiliyan’s situation in due course and we have moved quickly to support him and his family,” the statement said.
“During this time we ask that Stiliyan’s privacy is placed ahead of all inquiries and trust that we will share information as we receive it.
“Stiliyan is cherished by many and he will get from Villa every ounce of love and support that we have to help bring this to a positive conclusion.”
Petrov joined Aston Villa in 2006 after a seven-year spell at Celtic.
Meanwhile, Arsenal manager Arsene Wenger vowed to appeal as he was given a three-match ban by UEFA following a charge of improper conduct during a Champions League game.
Wenger, who was also fined 40,000 euros, will miss Arsenal’s next three European matches following the suspension, which stemmed from a confrontation with referee Damir Skomina after the Gunners’ 3-0 win over AC Milan on March 6.
Speaking just before his punishment was confirmed, Wenger said he would appeal if hit by a suspension.
“If I am suspended then it is not justified and I will appeal straight away,” Wenger said. “I believe that they have transformed UEFA competition referees to be untouchable icons, where you cannot even have a word.
“The only thing they understand after the game is the report.
“I believe that when you have 25 years consecutively in Europe you can still ask the referee that you can have some discussion with him. It is very difficult to understand.”