Leukemia's a cancer of the WBC (White blood cells) and once your immune system goes down you're susceptible to all kinds of diseases and sadly Aston Villa's Captain was diagnosed with it. 
Stiliyan Petrov:
Signed for Aston Villa in August 2006 in a £6.5m move from Celtic, becoming then-boss Martin O'Neill's first buy at the club.Has since made 219 appearances for the club, scoring 12 goals.Made captain in the 2009-10 campaign, leading the team out at Wembley twice.During his time at Parkhead he made 288 appearances, scoring 64 goals, winning four Scottish titles.Has won more than 100 caps for Bulgaria.

Source: BBC

On behalf of everyone in footyroom, we hope and pray that he'll keep fighting on just like Muamba did! Stay strong Petrov.

I can't believe what's happening, first Abidal, then Fabrice Muamba and now this. Sad news, hope he pulls through it and makes a full recovery. Pray for Petrov.

Sad news for football fans :( 

not a great year for football...

Stylian Petrov, announced that he will retire from football in order to focus on his battle with cancer :( Really sad for him, such a great player he was.

yeah, petrov is retiring :( sad year for football. get well soon stylian petrov. just something to say though, marijauna could cure 
Leukemia

Get well soon Petrov, really good player and such a shame

I missed it but supposedly he got a standing ovation before the Chelsea game and he was in tears.

The most important is that he's alive,no matter he plays or not.

He was a great football player!!!!

Hope your treatment goes well , get better soon !