De Jong, 31, made 15 appearances (eight starts) during his lone season with Cincy. He didn't register a goal or an assist in 793 minutes before his contract option was declined for 2021, making him a free agent.
Before joining Cincy, de Jong made four Eredivisie and four Champions League appearances with Ajax in 2019. He spent the 2018-19 season on loan in Australia with Sydney FC, providing four goals and three assists in 15 league appearances. De Jong originally made his debut at Ajax in 2007, starring at the club until joining Premier League side Newcastle United in 2014. He made 277 appearances for Ajax, adding 88 goals and 52 assists. He has also featured for PSV Eindhoven.
De Jong has made six appearances with the Dutch national team, scoring twice. He hasn't featured for the Oranje since a November 2013 friendly against Colombia.