Nunez was brought off under an hour into his match-winning display against West Ham in midweek, with Klopp explaining after the game that there were concerns over his hamstring.
“With Darwin, at half-time, everybody said ‘no it’s fine, it’s fine’,” the manager said, “but when somebody is five minutes on the bed then I’m concerned as well.”
Klopp described the substitution, which saw Nunez replaced by Harvey Elliott, as a “precaution.”
But the Uruguayan was not involved in outdoor recovery work at the AXA Training Centre on Thursday, and in his pre-match press conference, Klopp was unsure whether he would be available or not at Forest.
“He’s one of these we have to check now,” he told reporters.
“He had treatment yesterday and we will see what I get told later.”
It is largely positive news for Liverpool, however, with no obvious injuries emerging from the 1-0 win at Anfield, leaving only Ibrahima Konate, Naby Keita, Diogo Jota, Luis Diaz and Arthur as confirmed absentees.
“No injuries, but two tough games in short succession and now the next one coming up,” Klopp continued.
“So we need to have a closer look, who we can start again or who we can start.
“But it’s really close, we only have the session this afternoon. Yesterday was recovery for the boys who played the other night and today will be now the only session that we have.
“I will get all further information a bit later before training and we will see.”