Millsap, a first-time All-Star selection averaging 17.6 points and 8.3 rebounds in his first season with Atlanta, was injured late in the fourth quarter Friday at Detroit as the Hawks lost their eighth straight.
Pittman has 48 games of experience over parts of three seasons with Miami and Memphis. He appeared in 17 games this season for the NBA D-league Austin Toros.
Cunningham appeared in just five games with the Hawks. He spent most of the season playing for the D-League Bakersfield (Calif.) Jam.