Originally scheduled to arrive on Tuesday, the Ghanaian rejoined the Foxes on Wednesday morning, after playing every minute of Ghana's march to the semi-finals of the just-ended Africa Cup of Nations in Gabon.
Fascinatingly, the 22-year-old was selected in Ranieri's starting XI for the FA Cup encounter later on Wednesday evening, going ahead to play the entire duration of normal and extra-time at King Power Stadium.
“It was good to see the players who haven’t been involved so much play well and play with personality," Ranieri said, as reported by his club's official website.
"[Bartosz] Kapustka played well.
"[Yohan] Benalouane and [Marcin] Wasilewski were good and if you can imagine, Daniel Amartey arrived at 5.30am [on Wednesday] and played 120 minutes. Unbelievable.
“It was important to see how new players played.
"Often we play at the training ground, but it’s another thing to play in the FA Cup against Derby.
"They played face to face and we scored more than them."
Having endured a series of recent disappointments, Leicester will be boosted by Wednesday's win ahead of the Premier League clash with Swansea City on Sunday.
Amartey, who joined the Foxes last year, made 17 English topflight appearances this season before departing for the Afcon, and will look to pick up from where he left off on Sunday.
He played five times in the historic league triumph last season.