Sheffield United: Reds set to field Jurgen Klopp's 'best ever signing' at Bramall Lane

Despite lavishing millions on the likes of Virgil van Dijk and Mohamed Salah, Klopp described Joel Matip - a player he acquired for nothing from Schalke 04 - as an "incredible" piece of business ahead of the visit to Bramall Lane.

"In a world of big transfer fees, to sign a player like Joel Matip on a free transfer is incredible," said Klopp.

"It was maybe one of the best pieces of business we did in the last few years. Joel was always an incredible talent. He played as an 18-year-old boy for Schalke in the Bundesliga.

"It's a strong league and he played there, and was always a standout player, a fixed point in defence. Yes he lacked a little bit of consistency, that can happen especially with his physical stature.

"He doesn't always look sensational when he moves. But he grew and developed. Joel is in a really good moment; long, long may it continue."

Matip, a Cameroon international, is expected to partner van Dijk at the heart of Liverpool's defence when they meet a United side hoping to become the first team to beat them in Premier League competition since January. Confirming striker Sadio Mané is available for selection after recovering from injury, Klopp admitted goalkeeper Alisson Becker will miss the trip to South Yorkshire as he recuperates from a calf problem.

"Alisson looks like he is close, but the final word is with the medical department," Klopp said.."He's not in contention (to face United). Maybe he can train with the team from Sunday on. Really close."