The score was 1-1 when the Ivory Coast central defender fell backwards onto the pitch 18 minutes from time and had to be taken off on a stretcher.
"First and foremost he's okay, which is the most important thing," De Rossi told a press conference on Wednesday before Roma host AC Milan in the second leg of their Europa League quarter-final on Thursday.
"He's as good as a lad who's just suffered a collapsed lung can be. It's an ordeal, it's painful, but it's not as scary as we'd imagined it to be in the heat of the moment."
After a lengthy delay, Sunday's fixture was suspended and the players left the field, with the game later abandoned.
"We received a lot of praise for something that we deemed to be a standard course of action... I hope that any coach would've acted as I did," De Rossi said.
"Any player faced with the prospect of having to continue a match would have tensed up, knowing their teammate had suffered such an injury or, as the guy with the electrocardiogram had told us, that Evan was in the process of suffering a heart attack."
Ndicka remained at the hospital overnight and further tests ruled out a heart condition before he was discharged on Monday.
"When such a situation is up in the air - out of respect for your fellow professionals, everyone involved, and the paying public - it's not about setting an example, it's about doing what's right. We all agreed on this," De Rossi added.
"None of the players wished to proceed with the match, and it wasn't my call to abandon the fixture, as has been written. It was a collective decision, backed by the club.
"It's nice to be reminded of what a family we are in such moments, not just when we win matches."
The date when the remainder of Roma's match against Udinese could be played has not yet been decided.
"We know there are various options, different dates - although not that many, to be honest," De Rossi said.
Fifth-placed Roma host Bologna, in fourth, on Monday, before they face champions Napoli, Juventus and Atalanta in the following weeks.
