By David Winning

SYDNEY--Coles Group said it is in talks to acquire Greencross Pet Wellness Co. from private-equity firm TPG Inc., signaling a desire to expand its retail footprint beyond supermarkets in Australia.

Coles, which has a market value of around $21.68 billion, said it has begun due diligence but didn't signal what a transaction could be worth.

"As one of Australia's leading retailers, with a strong balance sheet and debt capacity, Coles regularly assesses strategic opportunities that may complement its existing business and create value for shareholders," Coles said in a regulatory filing on Monday.

TPG completed the acquisition of Greencross, which owns vet clinics and pet shops, in February 2019 for some A$675 million.

Write to David Winning at david.winning@wsj.com