He is the full-back with as many league goals as Victor Osimhen and more assists than Bruno Fernandes and Martin Odegaard combined. Alejandro Grimaldo has been one of the signings of the season. Best of all for Bayer Leverkusen? He cost them nothing.

The 28-year-old, a free transfer from Benfica in the summer having run down his contract with the Portuguese champions, has played a crucial role in Leverkusen’s ascent to the top of the Bundesliga, where Xabi Alonso’s side sit unbeaten, dreaming of a first title.

He boasts a phenomenal highlights reel. His tally of seven Bundesliga goals includes two sensational free-kicks, one of which came in September’s 2-2 draw with Bayern Munich, the side they meet again in Saturday’s crucial title showdown, live on Sky Sports.

His outstanding ball-striking ability shines through in every one of his goals and in many of his nine assists too. His trademark is a low cross flashed towards the far post from the left-hand side of the box. But his set-piece deliveries are just as likely to result in a goal.

His total of 16 goals involvements puts him well clear of any other full-back in Europe’s major leagues, next on the list being Jeremie Frimpong, his Leverkusen counterpart. Factor in all players and he ranks in the top 20 in a list otherwise dominated by forwards.

His impact at Leverkusen should come as little surprise. Alonso has helped by using a back three, allowing Grimaldo to play as a wing-back. But he racked up similar numbers across seven and a half seasons at Benfica playing primarily as a left-back in a four.

Grimaldo helped Benfica win four Portuguese titles in that time. There were links with Premier League sides, Arsenal, Liverpool and Manchester City among them. His former club Barcelona were said to be interested too. But their loss is proving Leverkusen’s gain.

Simon Rolfes, the club’s sporting director, describes him as a “simply incredible footballer, technically great and very intelligent”. He adds: “Part of the reason why we dominate games to the extent we do at the moment is to do with him reading situations very quickly and coming forward to create overloads.”

That combination of intelligence and technical guile comes up repeatedly in conversation with Andres Carrasco, the former U14 coach in Barcelona’s La Masia academy who oversaw a crucial period in Grimaldo’s career following his arrival from Valencia.

“At his previous club, he had been playing more centrally, as a midfielder,” Carrasco explains to Sky Sports. “But he was a player with really strong tactical understanding. We were looking for a left-back at that time, so we decided to move him.”

Carrasco describes Grimaldo as “the last piece of the puzzle” in a formidable academy team that included one-time Sergio Busquets successor Sergi Samper, ex-Arsenal duo Hector Bellerin and Jon Toral, and winger Keita Balde, who would go on to play for Lazio, Monaco and Inter Milan.

“Normally, these types of midfield players don’t like to move to full-back,” he said. “But his approach to the challenge was really good. He made it look easy because he was a smart and tactical player. He gave us a very dynamic left-hand side. He could find solutions easily.

“The defensive side was the biggest challenge.” Grimaldo was small in stature and stands at only 5ft 6in now. “But he had the intensity for it. You didn’t see him struggling because he was quick, he was energetic. The profile of a full-back was perfect for him.”

And yet it is his history as a central midfielder, coupled with his technical schooling in Barcelona academy, which best explains the extent of what he is now offering Leverkusen.

There are overlaps, cut-backs and crosses. But Grimaldo also comes inside to dictate play centrally. Only six players have made more final-third passes in the Bundesliga this season. None are full-backs.

His character is another strength. “His level of self-confidence was always very high,” said Carrasco with a chuckle. “He was excellent with his team-mates. Polite, attentive. But he also considered himself to be very good and that helped him.”

It certainly helped when making the decision to leave Barcelona aged 20. Grimaldo had captained their B team in Spain’s second tier. He was seen by many as a future first-teamer. But, seeing his pathway blocked by Jordi Alba, he was not willing to wait.

“Many players at that time at Barcelona had the same problem,” said Carrasco. “You might have to wait four or five years without making regular appearances, so if you want to play sooner and reach your maximum level, you have to make a decision.”

Grimaldo blossomed at Benfica. But recognition in his homeland was slow to follow. It was only in November of last year, a month after his 28th birthday, having made his move from Portugal to Germany, that he finally made his debut for the national side.

Why did the move to a truly top league not happen sooner? “When you are enjoying it at your club, when you are having good performances week after week and playing in the Champions League every year, you probably don’t want to move,” said Carrasco.

“Obviously, the right offer and the right situation has to come. We know Barcelona were interested in him. Other clubs too. But Benfica is a massive club. A top club in Europe which consistently wins trophies and reaches the group stages of the Champions League.”

Grimaldo was in no rush to leave, then. But the other side to it is that his suitors, particularly in the Premier League, had reservations about his physical attributes, chiefly his height.

“Of course, people talk a lot about the competition in the Premier League being much more physical, and Grimaldo, although he has good conditions, is not tall,” said Carrasco.

“But he is very dynamic and the full-back position is probably the one that has evolved most in football. You need quality there, a smart player who can make good decisions under pressure, in different areas of the pitch. I’m not sure height is that important.”

Leverkusen would agree given how Grimaldo has handled the defensive side of his role this season. He is above all an offensive outlet but, in a side that has only conceded 14 times in 20 games, there is little evidence that he is a weak link at the other end.

According to Opta, he has only been dribbled past 13 times in his 20 appearances. His total of 32 tackles is second-highest among Leverkusen players. He does not contest many headers but he is tenacious in duels and disciplined when it comes to tracking back.

It is just another way in which Leverkusen are feeling the benefits of his arrival. Grimaldo, overlooked at Barcelona and passed up by the Premier League’s elite, is finally gaining the recognition he deserves.

Watch Bayer Leverkusen vs Bayern Munich live on Sky Sports Football on Saturday; kick-off 5.30pm