BEIJING—Chinese food delivery giant Meituan warned it could be required to pay “a significant amount” of antitrust fines and posted a third consecutive quarterly loss on Monday as it continued to invest in expanding its various businesses. Meituan, China’s eighth largest company by market value, has faced regulatory heat as authorities crack down on the country’s sprawling platform economy. China’s State Administration of Market Regulation (SAMR) launched an antitrust probe into the company in April, focussing on forcing restaurants and other merchants to use its platform exclusively. SAMR also said on Monday it would further regulate the sharing economy sector and that it has been investigating Meituan not reporting its acquisition of bike-sharing startup Mobike in 2018 for antitrust review. Meituan said in its earnings report that it was actively cooperating with SAMR in the ongoing investigation and that it could be required to “make changes to its business practices …