(NewsNation) — The brother of imprisoned American Paul Whelan believes a potential prisoner swap with Russia is still likely months away from becoming a reality.

Russia and the United States said on Friday they were ready to discuss a prisoner swap, a day after a Russian court sentenced basketball star Brittney Griner to nine years in prison for a drug offense.

Paul Whelan’s brother David said he’s cautiously optimistic a prisoner swap could finally bring him home.

“I think we’re still probably months away,” he said. “But I think the U.S. has made a serious concession in what has been reported in the media. And hopefully, the Russians will go for it.”

Washington has offered to exchange Russian arms trafficker Viktor Bout for Griner and Whelan, sources familiar with the situation have told Reuters.