The 84-year-old, who was conducting the National Orchestra of France, lost balance during a movement of Tchaikovsky's Symphony No. 6.
The orchestra's website says he's expected to be released soon, following overnight tests.
In a statement Friday, President Nicolas Sarkozy sent his best wishes, calling the German-born Masur a "legendary musician."
Sarkozy also recalled the conductor's political engagement, and his "historic role" in helping reconciliation between East and West Germany at the time of the Iron Curtain.
