The condition was diagnosed in tests after the Aston Villa and Bulgaria captain, 32, developed a fever following last Saturday's 3-0 defeat against Arsenal.
The player, who won his country's Footballer of the Year award in 2003 when he was playing for Celtic, booked into a London hospital for immediate treatment last night.
Goodwill messages from across football, in particular from north of the Border, have been sent to Petrov, who was affectionately known as Stan after being signed for Celtic by John Barnes in the summer of 1999 for £2 million.
Former team-mate and Celtic boss Neil Lennon said he was "absolutely inconsolable" over the news, adding: "As a member of the Celtic family, it is important for Stiliyan to know that he has our unequivocal support in battling against this disease. Knowing Stiliyan as I do, and the many obstacles he has overcome in his life to get to the peak of his career, he will overcome this one too."
Lennon's coaching staff of Alan Thompson and Johan Mjallby, both former team-mates of Petrov, are said to have been left stunned by the news.
Aston Villa manager Alex McLeish, who posted a "get well soon" video for his captain on the official Aston Villa website, said his captain was "typical Stan-defiant" and "concerned about how it has affected his loved ones". "This is the first day of his recovery," he said.
"He is the captain, a leader, a defiant guy. He has fought many battles on the pitch before and I'm sure this is one he will win."
Of the other players, McLeish added: "They are gutted but galvanised to try to win this game [against Chelsea] for their captain tomorrow. I am sure he will be rooting for the lads tomorrow.
"He is a well respected player both in his time with Celtic, with Bulgaria and at Aston Villa. I knew him well in my Glasgow days. Stan was never anything other than polite and humble."
Petrov has been married to Paulina for 11 years. They have a nine-year-old son, Stiliyan Junior, and another boy, five-year-old Christian.
The couple, who were childhood sweathearts, are regarded as Bulgaria's answer to David and Victoria Beckham in their homeland, where Paulina is a highly sought-after model.
Petrov's early days in Glasgow are the only time the couple have been apart for a lengthy spell, and the footballer took to working in a burger van run by a friend to combat his loneliness.
He credits his interaction with customers for helping him learn the Glasgow dialect, enabling him to take part in dressing room banter with his Scottish team-mates.
Aston Villa supporters who had planned a protest today against the performance of McLeish, a former Rangers and Scotland manager, have cancelled their demonstration out of respect.
A statement from Aston Villa said: "We expect to learn more about Stiliyan's situation in due course and we have moved quickly to support him and his family.
"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 spent seven years and won four Scottish Premier League titles at the Parkhead giants. He left to join Villa for £6.5m in 2006 and has scored 12 goals in 219 appearances.