Celtic manager Neil Lennon has said that it was "a pleasure" to play alongside Stiliyan Petrov, who announced his retirement from football on Thursday morning.

Lennon, who considers Petrov a good "friend", hailed the Bulgarian's achievements in the game but admitted that health comes before anything else.

"Obviously it's very sad that Stiliyan has announced his retirement from football," Lennon told the club's official website. "He was a fine footballer and enjoyed a magnificent career at Celtic and Aston Villa, as well as representing and captaining Bulgaria on many occasions.

"First and foremost, of course, is his health, and the news earlier this year that Stiliyan is in remission was a great boost for everyone. I'm sure that Stiliyan's characteristic determination, along with the fact he's surrounded by a loving family, will ensure he's a success in this next stage of his life.

"The words he has spoken today demonstrate his absolute courage and positivity and show exactly the kind of man he is. It was a pleasure to play alongside such a great footballer, but, for me, I'm even luckier to call him my friend."

Petrov announced that he would be focusing on setting up a foundation to help others deal with leukaemia.