Each have been diagnosed with sprained ankles, Lopez his right, and Blatche his left. Tim Bontemps of the New York Post says that he does recall a play where Blatche could have tweaked his ankle, but doesn't really remember Lopez hurting his. Jason Kidd does believe he knows when, though.
Jason Kidd thought Brook might have tweaked his ankle early in the game when he fell in front of the Nets' bench.— Tim Bontemps (@TimBontemps) November 4, 2013
This play was early on in the game, so it clearly didn't stop Lopez from playing. He finished with 21 points and 6 rebounds on 8-of-15 shooting in the Nets loss to the Magic.
This is just a precautionary measure by the Kidd and the Nets as they don't want Lopez to have another issue with his surgically repaired foot, but they don't believe is connected to this injury. Both are expected to play tomorrow night despite their injuries.