Petrov's condition was diagnosed following tests after the Bulgarian international developed a fever following last Saturday's 3-0 defeat at Arsenal. Messages of support for the former Celtic player, known as 'Stan', have flooded in since the news was confirmed in a Villa statement on Friday afternoon.
McLeish said: "I spoke to him and he was typical Stan, defiant, but I think obviously he's concerned about how it has affected his loved ones. He's a captain, he's a leader, he's a defiant guy and he's fought many battles on the pitch and I'm sure this is another one he'll win."
He added: "We certainly think it's in the early stages and Stan will get the best medical attention possible."
Petrov's representatives confirmed the player was booked into a London hospital and will begin his treatment programme after the weekend.
Villa chairman Randy Lerner said: "We are completely focused on Stiliyan and his family. Stiliyan is someone who is cherished by many people throughout football.
"Every ounce of love and support that we have, he will get from the club to help bring this to a positive conclusion."
Celtic boss Neil Lennon, a former Bhoys team-mate of Petrov, said: "We are all absolutely devastated to hear this news.
"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."
Source: PA
Source: PA