Barron has played parts of four seasons with New York and Miami. The 7-footer appeared in seven games for the Knicks last season, averaging 11.7 points and 11 rebounds.
Lopez is expected to miss several weeks after spraining two ligaments in his left knee against the Lakers on Sunday night.
Lawal was the 46th-overall pick of this year's draft, but did not appear in the regular season for the Suns. Janning, a member of the Suns' 2010 summer league team, also didn't play during the regular season.