"Tonight was an absolute embarrassment," the veteran blue-liner said, according to The Athletic's Joe Smith.
The Preds controlled 62% of both the high-danger scoring chances and the expected goals at five-on-five, per Natural Stat Trick.
"This was one of the worst performances I've seen in a Lightning uniform from our group," said McDonagh, who joined Tampa prior to the 2018 trade deadline.
He added it was "not even close" to halfway effort.
The Lightning will get a chance to rebound on Thursday against the Florida Panthers.
Meanwhile, the Predators are arguably the hottest team in the NHL, as they've compiled an 11-2-0 record in their last 13 games. They've been banged up for a good portion of this stretch, too. Filip Forsberg, Matt Duchene, Eeli Tolvanen, and Dante Fabbro were among those missing from Tuesday's lineup.