The Frenchman has been out of action since March after being injured in their Champions League game against Shakhtar Donetsk with an initial recovery estimate of a few days.
Six months on and Bayern can still not provide a comeback date for Ribery, who has admitted to being frustrated by the slow recovery progress.
"It is now mid-September and I think that will be the case, that during 2015 he will be a whirling again," Rummenigge told reporters.
"What was important is to have the right diagnosis and treatment. I am not that pessimistic and I think in the not too distant future he will come back. That of course does not mean this week or next week," Rummenigge said.
"But he will come back. I am fully convinced of that and that is the key thing."
The 32-year-old has missed the final stretch of their league title-winning season as well as the entire pre-season preparation as he still struggles with the injury.
New signing Douglas Costa has been in superb form in Ribery's natural position, making any quick return to the starting lineup even more improbable.
Bayern, who also have fellow winger Arjen Robben out injured, are level with Borussia Dortmund on 12 points at the top of the Bundesliga and kick off their Champions League group stage with a game at Olympiakos in Piraeus on Wednesday.
(Reporting by Karolos Grohmann; editing by Sudipto Ganguly)
