Petrov, 32, has been diagnosed with acute leukaemia and this week started his treatment at a London hospital. The Bulgarian has been visited by Villa owner Randy Lerner, chief executive Paul Faulkner and manager Alex McLeish as a show of support.
With Petrov currently unavailable for selection, Villa have announced striker Agbonlahor as their new skipper. The forward, 25, has scored six times for the Villans this season, having emerged through the team's youth ranks to become a regular in the first-team.
McLeish's Villa, who take on Liverpool this weekend, are in poor form having won just one of their last eight Premier League matches, and sit just five points above the relegation zone.