Rooney, who has since managed to quit gambling, decided to speak out about the problem after facing criticism over Derby's decision to give him the number 32 shirt in association with a betting sponsor.
"It was easy to place bets by phone. It didn't feel like real money. It wasn't like I had to go into a bookies and put bets where there are limits," he said. "Before you know it you've lost a good bit and you don't realise the amount you're putting on at the time. I won at the start and thought it was easy money. It sucks you in a bit more and I ended up losing, ended up down.
"I was chasing my bets trying to win my money back. You're there to play for your country or club and when you're losing money the way I was, then it will affect you. "Thankfully I managed to pay up what I lost and I didn't gamble again. I've learned from my mistakes. If you carry on gambling, you lose more. That's when you can get sucked into a bad situation."