Robert Lewandowski's revival has been key to Barcelona's strong start to life under Hansi Flick as the striker returns to Dortmund to face Borussia in the Champions League on Wednesday.
The 36-year-old Pole has netted 23 goals in 21 games across all competitions this season, taking Barcelona top of the Spanish league and up to third in the European standings.
They lead last year's Champions League finalists Dortmund, who like Barcelona have four victories from five games, on goal difference before their meeting in Germany.
Lewandowski cut his teeth in top-level European football with Dortmund between 2010 and 2014, driving them to the 2013 final, where they lost to rivals Bayern Munich at Wembley.
A year later, he joined Bayern and finally claimed the Champions League with them in 2020.
Lewandowski arrived at Barcelona in 2022 and after a strong first campaign, his performance dipped last season.
Flick's arrival gave both the team and the veteran striker fresh impetus and, until a recent wobble in form, both have thrived.
Lewandowski reached a career century of Champions League goals in Barcelona's 3-0 win over Brest in November. He trails only all-time top goalscorer Cristiano Ronaldo and former Barcelona great Lionel Messi.
Lewandowski is top scorer both in Spain and in the Champions League, where he boasts seven goals from five matches, two more than any other player.
Despite his lethal form in front of goal, Lewandowski's presence in Barcelona's side does have one drawback.
PRESSING DOUBTS
In part, given his age, the striker has not been able to maintain his team's objective of pressing opponents as consistently as Flick would like.
A drop in pressing intensity has recently exposed Barcelona's high defensive line more than at the start of the season.
"It's clear that we made mistakes, but I insist, it's not the fault of the back four, it starts up front," said the coach after a shock 2-1 loss to minnows Las Palmas in LaLiga at the start of December.
Barcelona also recently threw away a two-goal lead at Celta Vigo, with Real Madrid gobbling up the distance between the sides at the top of the table that the Catalans had established.
Barca's recent issues will be thoroughly analysed by Dortmund ahead of the clash at the Westfalenstadion, with Flick also admitting his team have struggled on the road.
Barcelona twice let a lead slip in a 2-2 draw at Real Betis on Saturday in which Lewandowski scored. They were overwhelmed at times by the hosts.
"We have the quality to win every match but we also have to show that," said Flick.
"(In) the away matches we have to be much stronger than we played here."
Given Flick's drive to make Barcelona a more robust team, the questions is how long Lewandowski can continue to shine as the minutes rack up.
The coach rested the striker for a recent 5-1 romp over Mallorca which suggested Barcelona might not be dependent on the forward in the same way they are on 17-year-old winger Lamine Yamal.
However, Flick has backed Lewandowski since arriving and even if the Pole's work-rate has dipped, the coach believes.
"Robert is an absolute professional player, working hard on his fitness, this body he has, it's not this age," said the coach earlier in the season.
After some frustrating displays last season, Lewandowski has rolled back the years under Flick and Dortmund fans will fear the return of the devastating forward who wore their colours a decade ago.