The Collaborative International Dictionary of English v.0.48:

denigrating \denigrating\ adj.
   harmful and often untrue; tending to discredit or malign; --
   used of statements.

   Syn: calumniatory, calumnious, defamatory, denigrative,
        libellous, libelous, slanderous.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

denigrating
    adj 1: (used of statements) harmful and often untrue; tending to
           discredit or malign [syn: calumniatory, calumnious,
           defamatory, denigrative, denigrating,
           denigratory, libellous, libelous, slanderous]