The 22-year-old, who was to play the final game of his loan spell on Saturday, will now remain at Spotland until January 5.
Gornell joined Rochdale on November 9 and has netted once in four appearances for the club.
Manager John Coleman is delighted to have secured the services of Gornell for another month. He told the club's official website: "He's a good player and he brings something different to our game.
"I thought he had one of the better performances on Saturday against York City and he's getting better with each game he plays."