The 72-year-old Heynckes led Bayern to the domestic league and Cup double and the Champions League title in 2013 but then made way for Spaniard Pep Guardiola.
Italian Ancelotti took over last season but was fired after Bayern slipped to second place in the league, twice squandering two-goal leads in consecutive games. They also went down 3-0 at Paris St Germain in the Champions League.
"Nothing has been finalised. I still have to analyse everything because it has been four and a half years since I last worked for Bayern and football has changed since then," the Heynckes told the Rheinische Post newspaper.
He said Bayern had made an offer until the end of the season and he had met with club bosses to discuss "several issues", adding he felt fit enough to do the job despite his age.
He did not say when he would make his decision.
Heynckes, who also led Real Madrid to the Champions League title and coached Benfica, Athletic Bilbao and a string of Bundesliga clubs, has not worked since 2013.
He also coached Bayern from 1987-91 and briefly took over at the end of the 2008/9 season before becoming head coach between 2011 and 2013.
(Reporting by Karolos Grohmann; Editing by Greg Stutchbury and John Stonestreet)
