Hi Satochan; We may have signed him, but there has been no official announcement.
Generally Juve has a policy of not commenting on transfers before they're official. At this point of the season I think it's particularly wise, because some of the players game might be infected if they knew a class player were joining next season to rival their place in the team.
Having said that I'm certain Athirson's agent would have been in the media by now if this had fallen into place. Maybe Juve persuaded him to stay quiet- who knows ?