Liverpool manager Jurgen Klopp has hailed unsung hero Joel Matip (below) as one of the best signings he has made.
In his four years at the club the German has broken the club's transfer record twice with the signings of Mohamed Salah (£38million) and Virgil Van Dijk (£75million).
He has made five other £30m-plus signings but believes free transfer Matip was the best deal.
"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 will start against Sheffield United today, keeping Joe Gomez and Dejan Lovren out of the side again, having put together an impressive run of form.
He has partnered Van Dijk in central defence for every match since January 19 bar four games last season and just the Community Shield and European Super Cup final this campaign.
The 28-year-old had a clause in his contract triggered earlier this month which ties him to the club until 2021.
Klopp is also keen to keep the veteran in his squad James Milner, who turns 34 in January, for the foreseeable future.
The midfielder, who played a key role in Wednesday's League -Cup win over MK Dons with a goal and an assist, is in the final eight months of his contract but his manager believes there is plenty of life left in the player yet.
"Milly is unbelievably important. He is Mr Professional, that's how it is. He's very serious in all the things he does, but very funny in the dressing room," added the Reds boss.
"He's a role model for the young boys. Not only the young boys actually. He's had an exceptional career so far and he looks like he has a few more years in the locker. Contract situations, we don't talk about here. But we are really happy to have him."
Klopp was also happy with the current injury situation with goalkeeper Alisson Becker expected to make his long-awaited return to first-team training on Sunday.
The Brazil international has been sidelined with a calf injury since the opening match of the season on August 9.
"Alisson looks like he is close, but the final word is with the medical department," said manager Jurgen Klopp.
"He's not in contention for tomorrow. Maybe he can train with the team from Sunday on. Really close.
"Alisson's injury was serious but in the last two weeks he progressed really really well."
Sadio Mane has fully recovered from a dead leg sustained in last weekend's win at Chelsea while fellow forward Divock Origi has returned after missing three matches with an ankle injury, although midfielder Xherdan Shaqiri, who injured a calf in training on Monday, is not fit.
David McGoldrick is a major doubt for Sheffield United as they prepare to host the Premier League leaders.
The Republic of Ireland international has missed the last two matches with a muscle injury and, at his press conference on Thursday morning, Blades boss Chris Wilder was not optimistic about McGoldrick's chances of being fit for the Saturday lunchtime kick-off.
Fellow striker Billy Sharp is suspended and will serve the second game of a three-match ban but on-loan Everton midfielder Mo Besic returns to contention having been unable to play against his parent club last weekend.