Without the president, Uri will no longer be the ruling party, the Yonhap News Agency said.
The Grand National Party already outnumbers Uri in Parliament since 23 legislators jumped ship earlier this month.
Roh, as a president without a party, is unlikely to have any significant accomplishments in his last 10 months in office.
He plans to introduce a constitutional amendment that would allow presidents to serve two terms, giving them more of a chance to make policy. At present, they are limited to one term.