The former Celtic star could make a permanent move to Stoke in the summer for £1.5million - double the £750,000 Derby forked out for him.
Jewell said: "Stephen would not have gone if we had any chance of staying up.
"But any money we can save now will go towards helping us come straight back up. He's a decent player but I have to make these decisions for the long-term benefit of this club.
"It's a good move for him and it's a good move for us financially. The money we save from him going will go into the pot for next season.
"It will be ploughed into making a sustained Championship challenge."