according to the page he put up zetsu was inside him dumbassSpores don't go inside of your body DUMBASS.
again if u read he said he could've
"Base sharingan Sasuke had the zetsu spores (containing senju dna ) when he was unconscious after defeated Itachi.Obito had treated sasuke wounds ,this was a perfect time to insert zetsu spore in his body"
making this very possible