Klopp left Diaz out of his 20-player matchday squad for Sunday's Premier League clash with Nottingham Forest, citing the kidnapping as the reason why.
News filtered through from Colombia overnight that Diaz's parents had been kidnapped by armed men on motorcycles in their home town. The rapid response of Colombian authorities saw the player's mother released without harm, but his father has remained missing.
"We had to obviously make a late change because of the private situation involving Luis Diaz. It's a worrying situation for all of us and it was a pretty tough night. I have never had that before. It's a new experience I never needed," Klopp explained ahead of kick-off against Forest at Anfield.
The Reds had released the following statement on Sunday morning ahead of the match: "Liverpool Football Club can confirm it is aware of an ongoing situation involving the family of Luis Diaz in Colombia. It is our fervent hope that the matter is resolved safely and at the earliest possible opportunity. In the meantime, the player’s welfare will continue to be our immediate priority."