"A year ago I was just playing reserve-team football in front of 25 people," O'Brien told the Manchester Evening News.
"I can't believe what has happened to me so far this season. You always hope to get your chance, you dream about it, getting in and playing in the Premiership.
"I thought I would get a chance with a bit of hard work, although deep down you think it just might not come.
"Obviously, the gaffer - Sam Allardyce - knew of me from reserve matches, but going on loan to Sheffield Wednesday was great for me.
"When that chance did finally come, I was absolutely delighted."