Cudd was the man to be initially punished for a dangerous tackle on Falcons' No8 Adam Powell early in the second half but video evidence has since shown that it was Evans who was at fault for not returning Powell to the ground safely. The decision means that Cudd is free to play but Evans won't be available to feature until March 12.
"We had a disciplinary meeting on Tuesday night and Nic Cudd was exonerated but Dan Evans was banned," said Dragons director of rugby Lyn Jones.
"It's a blow. You have a plan and it's not easy to deal with when one of your key players is taken out of the equation. But we have to deal with it and we have to move on."
Evans has been in fine form for the region so far this season, featuring in 20 games and starting all but one of those fixtures.
And while the arrival of Lee Byrne and the promise of Wales youngster Hallam Amos means he wasn't offered a contract extension at Rodney Parade and will instead switch to the Ospreys in the summer, losing the twice-capped No15 for a total of four important league games is far from ideal for the Dragons.
Evans will be forced to sit out this Sunday's home tie with Edinburgh and a trio of tough-looking ties against Leinster, Glasgow and Ulster throughout February, with Amos and fly halves Steffan Jones and Jason Tovey his most likely replacements.