China's badminton world number one Shi Yuqi continued his indifferent run of form with a quarter-final loss to Hong Kong's Lee Cheuk-yiu at the Korea Open on Friday.
Shi ended double Olympic champion Viktor Axelsen's 131-week reign at the top of the rankings in June but the Chinese player has struggled to consolidate his position in recent weeks.
He lost in the quarter-finals at the Paris Games before being ousted in the semi-finals of last week's Japan Open by French teenager Alex Lanier.
Shi went down 21-13, 21-15 to world number 17 Lee in South Korea.
The 28-year-old Shi has won four tournaments on badminton's world tour this year.
Denmark's Axelsen is not competing at the Korea Open.