Metro is in talks with about five parties interested in the chain, which has annual sales of more than 7 billion euros (6 billion pounds), he told journalists late Thursday.
"We only talk to potential buyers who want to take on everything," Koch said, adding: "You can never rule out bidders forming consortiums."
People familiar with the matter said Kaufland owner Schwarz group had tied up with retail property investor X+Bricks AG led by former Corestate Chief Executive Sascha Wilhelm.
Separately, shopping mall operator ECE is working with Morgan Stanley Real Estate (MSRE) on a possible bid, the people said.
"We are following the discussions about Real's future very closely. However, we are not an operative retailer and do not want to become one," ECE said in a statement.
It remained unclear whether the ECE/MSRE consortium was working with a hypermarket group as an additional partner.
Schwarz, X-Bricks and MSRE declined to comment. Metro also declined to comment on interested parties.
Germany's antitrust watchdog is expected to view with concern a takeover of Real by one of the other large hypermarket groups as it could be seen as hampering competition.
Industry bankers have predicted Metro might have to effectively pay a buyer to take the chain off its hands.
Real runs 279 hypermarkets, of which 65 are owned by the group itself. One person close to the matter has estimated the properties to be worth 750-900 million euros, to be balanced against the expected negative value of the operating company.
Koch, who is being advised by JP Morgan and Bank of America on the transaction, has said he expects to achieve a positive purchase price on the deal.
(Editing by Emelia Sithoe-Matarise and Mark Potter)
By Matthias Inverardi and Arno Schuetze