The agent of the 21-year-old recently claimed that the Addicks had withdrawn their latest contract offer after the Cameroonian had previously turned down fresh terms.
Despite the dispute, Powell hopes that an agreement can be struck between the two parties.
"It's an issue that has been ongoing for a long time and should have been something that was resolved as soon as the season ended," he told Sky Sports News.
"We got very close last week and right at the last minute they changed it again. Ceddy is well within his rights to turn it down and his Dubai-based agent has advised him not to sign.
"I've told him how much I want him to stay. He's had two years here and he's a young man who has got the ingredients to be a good left-back. He's starting to show that. He hasn't really had a career yet and I want him to have that here."
Evina joined Charlton from Oldham Athletic in the summer of 2011.