The highly-rated playmaker agreed to join Bayern Munich for £32m earlier in the year and Riedle said that the club would still be able to cope without him.
"To be honest, it isn't at all easy to replace a player of Mario Gotze's qualities, as few in Europe are able to match him," Riedle told Bundesliga.com.
"He's an outstanding player and his departure no doubt is a bitter loss for the club. However, Borussia Dortmund have proved in the past what they can do even with Gotze unavailable.
"I have full faith in Jurgen Klopp and Michael Zorc. I'm sure they won't panic and will find the right replacement."
Gotze has been capped 22 times by Germany.