The cast of "Glee" was caught shooting the new season yesterday in L.A. -- and one of the shots holds what could be a clue about who's singing what on the all-Britney Spears episode.

Lea Michele was spotted wearing maroon sweats and a yellow sports bra ... which, as Perez Hilton points out, is the same exact outfit Brit Brit wore in the "...Baby One More Time" video!

The rest of the cast were all snapped on set as well with matching "New York City" t-shirts -- and they were reportedly heard singing Jay-Z and Alicia Keys' "Empire State of Mind," presumably for a different episode.

We'll find out for sure when the show returns September 21.

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