Liverpool defender Virgil van Dijk is already a "complete player" but can reach another level if he adds more silverware in his career, according to former coach Pascal Plancque.
The 27-year-old has emerged as one of Europe's premier centre-backs since completing his £75 million (€87m/$99m) from Southampton to Anfield.
Van Dijk's displays during his first six months at Liverpool saw him guide the team into the Champions League final, where despite defeat to Real Madrid he was eventually named in the Uefa Team of the Year.
And with the Reds in contention to win their first Premier League title for 29 years, Van Dijk is among the favourites to scoop the PFA Players' Player of the Year prize.
Plancque, who worked with the Netherlands captain for two seasons at Southampton under Claude Puel, believes he is one of the best defenders in the world but needs success to take the next step.
"For sure, he's the best defender I've worked with," Plancque told Goal of Van Dijk, whose three major honours came at Celtic, where he won the Scottish Premiership twice and the League Cup.
"Technically he's a monster, Physically he's a monster. He has everything.
"The titles will give him an extra dimension but he is already a very complete player. Maybe he should be aware of complacency, because he is so comfortable that he can lose his concentration, but I do not see any limits."
Among the defining features of Van Dijk's performances this season has been his physical dominance in both penalty areas.
He is in the Premier League top 10 for clearances, with 163, while in the attacking third he has contributed four goals in all competitions including a vital header in the Champions League win over Bayern Munich.
Already the skipper at international level, it appears to be a matter of time until he takes over the armband from Jordan Henderson on Merseyside.
"What strikes me first is his physique, he is very tall and very strong," added Plancque.
"He has a good head and exudes a lot of power, he also exudes a certain charisma, with personality.
"It translates into training, into the application that he puts to work. As soon as there was a competitive aspect, he wanted to win every game in training.
"He's a technical leader because he is very strong. He commands, he recites and encourages. It takes up space in a group. He has a big ego.
"Virgil is someone you shouldn't take lightly. It must be managed accordingly. In times when the opponent wins, he hates losing. he displays his bad mood."