And the Englishman wants to repay the faith shown in him by producing the goods for the Parkhead club this season.
"I was out the game for a year and a half," explained Blackman. "I spent my time at a soccer school, the Jamie Lawrence Football Academy, which you pay a fee for on a daily basis.
"You work like you're at a club. But, at one stage, I couldn't pay because I didn't have money.
"I got in touch with an agent and he said he would pay it for me. It was a big reality check.
"In fairness, it was what I needed to open my eyes. There were times it was really hard, but I had to show a bit of mental strength to get through it."
From adversity – and poverty – a new player has emerged.
He said: "I'm happier now because the whole thing has made me wiser.
"I was playing football with my friends at a local five-a-sides in London. That was it. There were no offers the whole time. Whenever someone heard the name Andre Blackman they said 'Nah, I don't fancy him'.
"Then a friend of the manager recommended me and asked if I could come up for a trial.
"I definitely appreciate this chance after everything I've been through. I was kicked out of football early on in my career."
Blackman, who started against Augsburg in the opening game of the tour on Tuesday, added: "I'm thankful Celtic have given me the chance to express myself. I know I have to grab it with both hands.
"This is an important season for me. Everyone wants to play, but it's down to the manager.
"There's a good set of backroom staff and a good manager willing to help me. If I'm going wrong, they can pull me aside and tell me what needs fixed. I've never had that at other clubs.
"I needed somewhere to go and show that I had changed and the views people had of me were wrong."