It could just be a container that has fallen off a ship," he said during a visit to Papua New Guinea. "We just don't know."
Abbott was responding to a question from a journalist about whether he had "jumped the gun" Thursday by publicly announcing the discovery of the possible objects in satellite imagery and the decision to send search teams to investigate them.
Meanwhile a Norwegian cargo vessel taking part in the search for possible debris from the missing flight has not uncovered anything overnight, a spokesman for the Norwegian Shipowners' Association said.
"I have just learned from the ship owner (Hoegh Autolners) that the vessel has not made any significant sighting so far today," Haakon Svane of the Shipowner's Association told broadcaster NRK early Friday.
Deutsche Presse Agenture quoted Svane as saying that visibility was expected to improve slightly compared to Thursday, Svane added. The Hoegh St Petersburg, which is transporting cars, has a 19-strong Filipino crew. The vessel was asked to take part in the search by the Australian Maritime Safety Authority.