The Titans made the deal for Johnson after their starting fullback, Ahmard Hall, was suspended for the first four games of the season for violating the NFL's policy against performance-enhancing substances.
Underwood, a third-year pro, has been slowed by a knee injury suffered during training camp. He also was switched from cornerback to safety.
Probably working against Underwood, too, were two off-the-field incidents in the last year. He pleaded not guilty this month to one count of disorderly conduct for an incident with his wife, and he pleaded no contest to a misdemeanor count of soliciting a prostitute in June 2010 at a resort cabin in Lake Delton, Wis.
Even with backup quarterback Matt Flynn expected to be a coveted unrestricted free agent after the season, the Packers apparently decided it was worth the risk of exposing Harrell to the waiver wire. Harrell, who seemed to please the Packers' coaching staff with his development in his second year with the team, is still eligible for the practice squad.
"The lockout probably hurt Graham the most of the three quarterbacks," quarterbacks coach Tom Clements said last week. "He works at it; he has a knack back there passing. The more he learns about the offense and the more he feels comfortable with it, that allows you to play better."
The other players released by the Packers on Saturday were wide receivers Diondre Borel, Tori Gurley, Kerry Taylor and Chastin West; safeties Anthony Bratton and Anthony Levine; offensive linemen Chris Campbell and Ray Dominguez; nose tackles Chris Donaldson and Jay Ross; linebackers Ricky Elmore, Cardia Jackson and Elijah Joseph; center Sampson Genus; cornerbacks Josh Gordy and Brandian Ross; fullback Jon Hoese; defensive end Eli Joseph; center/guard Nick McDonald; and running backs Dimitri Nance and Brandon Saine.
Defensive end Lawrence Guy (concussion) and wide receiver/kick returner Shaky Smithson (shoulder) were placed on season-ending injured reserve.
Packers general manager Ted Thompson didn't speak with reporters after the roster moves, which has been the case for several years now. Last week, he lamented the impending cuts.
"We've been with this group a short time -- this 2011 team -- compared to most years, but you have attachments and you like the kids," Thompson said. "This is a good group of guys. A lot of these guys have been training for these moments for a long time, so when you have to say goodbye it's a hard time."
The Associated Press contributed to this report.