Greenwood was sin-binned for a high tackle on Matty Lees during his side’s 18-6 win over his old club St Helens in Friday’s derby at the Totally Wicked Stadium and handed a two-match ban by the Rugby Football League’s match review panel.
Greenwood will miss the leaders’ next scheduled fixtures with Huddersfield and Leeds but will be free for the semi-finals on November 19 or 20.
The panel also gave a two-match suspension to Leeds forward Mellor for making late contact with the head of half-back Ryan Hampshire during the Rhinos’ 30-6 defeat by Wakefield last Thursday.
Meanwhile, Castleford forward Oliver Holmes avoided suspension after being sent off for kicking Leeds full-back Richie Myler in his side’s 28-24 defeat at Headingley last Monday.
Instead he was issued with a caution after the panel ruled he made only “light contact” on his opponent.
Leeds duo Myler and Robert Lui were also given cautions for foul play.
Listen to The Final Hooter podcast, featuring exclusive interviews, every week. SUBSCRIBE to Love Rugby League on Apple Podcasts.