New Forest manager Steve Cotterill struck an agreement with City earlier on Tuesday to bring in the 20-year-old left-back on a deal until the end of December.
Cunningham insists he did not hesitate to take up the offer and he is now looking forward to playing for such a prestigious club.
"I first became aware of Forest's interest midway through last week and had the weekend to think about it," Cunningham told Forest's official website.
"To be honest it was a no brainer. Forest is a massive club with a great history and tradition and it's an honour to have the opportunity to play for them.
"I'm delighted to be here and can't wait for Saturday's game against Hull."
