Why a very "special talent" is heading to Sheffield United on deadline day

“He’s an investment for our future,” the German legend said. “He fits the bill perfectly and attracted interest from all over Europe.”

But it was in Greece, where Retsos spent the first two seasons of his career before transferring to the Bay Arena, that the qualities which seduced someone of Voller’s stature first became apparent.

And, after agreeing to spend the rest of the campaign on loan with Sheffield United, the ones Chris Wilder believes will make the centre-half his shrewdest, if not highest profile, January signing.

Retsos, aged 21, still holds the distinction of being Olympiacos’ youngest ever captain after progressing through The Red and Whites’ youth system. The armband can be heavy at a club whose derbies against Panathinaikos are dubbed ‘The Mother of all Battles’. But Besnik Hasi, their manager at the time, was so impressed with Retsos’ leadership skills he decided it should be wrapped about the bicep of a player still six months shy of his 19th birthday.

Wilder, who spent yesterday finalising the terms of the centre-half’s move to Bramall Lane, views the youngster as the ideal solution to a problem which has troubled him since August.

Chris Basham, United’s preferred option on the right side of defence throughout their climb from the third to the first tier of English football, has performed admirably this term. But if injury or suspension made him unavailable for selection, there are no tailor-made alternatives.

Speaking ahead of tomorrow’s visit to Crystal Palace, Wilder also made numerous references to the importance of “genuine” competition.

“We aren’t bringing in players as ‘projects’ or anything like that,” he said. “I believe the lads already here want to see good players coming in because they know that makes us better and shows we’re ambitious and trying to keep heading in the right direction.”

Retsos, whose presence will provide Basham with exactly that, cost Leverkusen £15.7m when he left Athens in 2017.

Born in South Africa but capped five times by Greece - the country of his parents’ birth - he made an immediate impact under then manager Heiko Herrlich before suffering the first of two muscular complaints which subsequently stalled his progress.

Under contract until the summer of 2022, Retsos has been injury free for the past eight months and would fall within United’s budget if they later decide to try and test Leverkusen’s resolve to retain his services.

After capturing Jack Robinson from Nottingham Forest earlier this month, having also handed Jack Rodwell a short-term deal, Wilder believes United’s rearguard is now stronger than at any time since he took charge three and a half seasons ago.

They have prepared for the visit to Selhurst Park ranked eighth in the table, only a point behind fifth-placed Manchester United, and having spent around £22m to capture Norway midfielder Sander Berge.

“The boys who have come in and the ones we will be bringing in,” Wilder said, “Well, they want to be in there (the team) right now.”

Retsos was scheduled to complete the second half of his medical with United on Friday morning.