Originally Posted by
Assassin
Also, the same applies to gai. It's never been said that once you're team graduates, you get a new team rite away. He could just be a "free" jounin like neji and the others, doing missions (which is what thier real job is).
Not to mention that he could have a team, and still have been sent on this mission because he's uniquely qualified. He's one of the strongest jounin in konoha, he knows his team mates and thier strenghts/weakneses really well, he has experience facing akatsuki members before, as well as experience fighting against the sharingan.