The Millwall frontman joined the Robins last month and will now stay with the club until November 26.
He has scored one goal - against Oxford United in the Johnstone's Paint Trophy - in his six appearances for the club.
"John has given us energy and has been a real goal threat. I'm sure the goals will come and given more time he'll be good for us," Cheltenham boss Mark Yates told the club website.
Cheltenham are seventh in the League Two table with 15 points from their first nine games.