You can't blame her for being concerned!

Katy Perry "doesn't approve" of her pal Rihanna's decision to reunite with Chris Brown, and their once tight bond has suffered because of it, sources tell Us Weekly.

The "Fireworks" singer and the "Stay" crooner have been close for years, but the two apparently went out of their way to avoid each other at the Grammys last Sunday.

"They aren't tight anymore because Katy doesn't approve of Rihanna dating Chris Brown," the source adds.

The brunette bombshell chose to stick by her man John Mayer all night at the award show, while the Barbadian beauty put her love for Chris Brown on full display with some very public PDA!

It's so sad their friendship is struggling, but we're going to have to agree with Katy on this one!