According to The Telegraph's Chris Bascombe, he said: "I took Mo Salah off because he had a hamstring a little bit. Then everyone said, 'How can you take him off?' I do not go out and say 'Yeah, but he is close to being injured.' He is not at the moment, thank God."
Salah opened the scoring before being substituted in the 67th minute, 10 minutes before Wayne Rooney fired in a penalty to hand the Toffees a point.
Klopp also began the match with Roberto Firmino and Philippe Coutinho on the bench, and his decisions drew criticism from some pundits, including sports journalists Gary Al-Smith and Ian Abrahams:
Gary Al-Smith @garyalsmith
Even if LFC win this, look no further, again, than Klopp. You've got firepower. You use it. You don't have UCL this week. Why rest any of the quartet? Or sub Salah?2017-12-10 16:05:36
Ian Abrahams (Moose) @BroadcastMoose
Klopp started with Coutinho & Firmino on the bench and took Salah off before the Derby was won. Questions to answer for the Reds boss2017-12-10 16:06:03
The German confirmed the Brazilian pair were fit to start the match, but he added:
"We have a little information after a game, and sometimes that leads to a decision that sometimes you should not go with the risk of this player or that player. Sometimes you have to ignore [it] because the player has to go through. That is how it is. We have to make these decisions."
Klopp noted the need for rotation with the festive period bringing games thick and fast. The Reds still have five matches remaining in December, having already played three times this month, before playing again on January 1.
The manager explained why he elected not to reveal the thinking behind his decisions on Sunday despite the criticism he received:
"It would sound like an excuse. I do not want to deliver that. I do not need an excuse. I make the decision. You should know that after two years. I want to win the game 100 per cent, but on the other side I work with human beings and see them every day. I know if they have a sore throat, a knee problem or whatever."
Football writer Joel Rabinowitz felt the criticism was somewhat unfair:
Joel Rabinowitz @joel_archie
So, it turns out Salah got subbed due to a hamstring issue while Firmino & Coutinho were rested due to advice from the medical team. Almost like Klopp has more info when making team selections than people on Twitter.2017-12-13 10:36:08
Indeed, we're not always privy to the factors at play behind the scenes.
It's understandable he particularly wants to keep Salah fit given what he has achieved in such a short space of time at Anfield, per football writer Dave O'Connell:
Mohamed Salah since he arrived at @LFC: 🔴 Games: 23 ⚽️ Goals: 19 🏆 LFC Player Of The Month: 3 🔥 Goal Of The Month: 2 ⭐️ UCL Player Of Week: 2 🥇 PL Player of Month: 1 🏆 BBC African Player of the Year: 12017-12-11 18:05:52
The Reds can ill afford to lose him, particularly at a time in the campaign when even a minor injury could rule a player out for several matches because of how close together they are.
Klopp believes the evolving demands of the game will see rotation become more frequent at the top level: "It is quicker, more intense, with more sprints, more high runs, less breaks and so many things. It is going in one direction, and you have to react."
Liverpool will have been disappointed not to beat Everton, not only because it was against their local rivals but also because it was a highly winnable game.
However, while Klopp's team selection may have been partly responsible, his rotation could reap long-term benefits if it helps his best players stay fresh.