Nunez was withdrawn before the hour mark of the midweek win over West Ham United and narrowly missed out on recovering in time to face Forest.
Thiago, meanwhile, could not be involved due to illness.
Klopp told BT Sport pre-match at the City Ground: “No [it’s not precautionary], I wish I could do that.
“For Darwin the game comes too early, he still feels the intensity of the game muscle-wise so there was no chance he could play today. Maybe he could play tomorrow or on Monday but not today.
“And Thiago got a bad ear infection overnight. The decision was made this morning at 5.15. That’s how it is sometimes and that’s the reason for that.”