As reported in the link below, McCarthy has stated he'd like to keep 3 QBs on the 53 man roster (a departure from recent years), with a 4th. in development (read practice squad).
The 4th. guy would have to be raw and not particularly valued around the league otherwise somebody might snag him for their 53 man roster when we cut him in advance of signing him to the practice squad.
In the event this #4 is a pleasant surprise in preseason while Tolzien fails to progress, I believe Tolzien still has practice squad eligibility, if it comes to that, having been on the 45 man game day roster for fewer than 9 games.
As noted in said link, the Packers have scheduled a meet-and-greet with Brock Jensen, a somewhat unusual effort taken for a guy rated as the 25th. QB in the draft, well below the 7th. round cut line, by one respectable source (see second link below). Jensen, or someone of similar pedigree, is likely to be the #4 in camp.
With 90 camp slots, which I believe the Packers did not fully fill last year, maybe a 5th. QB is brought in as well to compete..
http://www.packersnews.com/article/...08029/Packers-schedule-visit-Waupaca-s-Jensen
http://www.nfldraftscout.com/ratings/dsprofile.php?pyid=94170&draftyear=2014&genpos=QB