Kyle Edmund will lose his status as British number one after being beaten in the first round at the Shanghai Masters - a sixth straight defeat.
Edmund is also set to drop out of the world's top 50 when the new rankings are announced next week after a 6-4 7-6 (7-3) loss to Frenchman Jeremy Chardy.
His last win came was against over Nick Kyrgios at the Rogers Cup in August.
Dan Evans or Cameron Norrie will replace the 24-year-old at the top of the British rankings.
Evans, beaten in qualifying in China, is currently set to do so, but third-ranked Norrie could still leapfrog them both after moving into the second round of the Shanghai Masters with a dominant win over Gilles Simon.
Norrie, 24, had qualified to reach round one and broke his French opponent twice to take the opener 7-5.
He then broke serve three times to take the second set 6-2 and faces Russian world number four Daniil Medvedev next.
Later on Monday, fellow Briton Andy Murray faces Argentine Juan Ignacio Londero.