 Having found opportunities in MLS difficult because of a persistent MCL injury, and having made just 1 senior appearance for Revolution against the Chicago Fire in his two years with the team, Oka signed with the Portland Timbers for the 2008 season, eventually featuring in 7 games and scoring 1 goal.He then signed for the newly promoted USL First Division side Cleveland City Stars for the 2009 season, and played 13 times for the team, before the club folded at the end of the season.Having been unable to secure a professional contract elsewhere, Oka signed with Vermont Voltage of the USL Premier Development League, scoring the winning goal in their opening match of the 2010 season.