Thon claims that the 28-year-old has lost his pace and cannot get past opposition players anymore.
"Schweinsteiger is a player who will only further decline simply because he no longer has the speed from before," he told Sky 90.
"You need speed and aggression in his position, although I have to admit that Schweini is doing a good job. He is showing other qualities and could perhaps stay at this level until the 2014 World Cup.
"After that, he will probably follow the same path as Michael Ballack with the national team. It could even [be] sooner. Schweini's mainly playing simple vertical passes and cannot beat his man anymore. Borussia Dortmund's [Ilkay] Gundogan brings more to the table at the moment."
Thon played for Bayern between 1988 and 1994.