Strikers being judged on goals is an unwritten rule of football. They were what made Sebastien Haller a fan favorite with Eintracht Frankfurt, where he shot himself to a prominence that has since produced two club-record transfers to acquire his services. 

They were, however, what went missing during a forgettable 18 months with West Ham before the Ivory Coast international rediscovered his touch with Dutch record titleholders Ajax — in record-breaking fashion no less.

Five goals in his first two Champions League games set the new best mark as he currently sits atop the competition’s goal-scoring charts in his debut campaign. On Tuesday, the 27-year-old pits his prolific wits against Borussia Dortmund, a side being touted as potential suitors when the time comes to replace their own star striker, Erling Haaland.

Fan favorite in Frankfurt to 'flop' with West Ham

It's not the first time Haller's name has been linked with a move to Dortmund. The club reportedly showed interest during his time in Frankfurt, where he was an integral ingredient in the blend of pace, precision and power that saw him flourish alongside Ante Rebic, Filip Kostic and Luka Jovic.

When the Eagles' band got broken up, Haller talked about "taking the next step" as he completed a €50-million (€43-million) deal to move to the Premier League in 2019. His fans, however, had to watch on as West Ham manager David Moyes failed to tap into his talents by misusing the qualities that made him a standout striker in the Bundesliga. 

As a result, he went from being part of one of the most prolific front lines on the continent to being labeled a "flop" on the back of 14 goals in 54 games for the Hammers, who jumped at the chance to offload him to Ajax after one and a half seasons. 

"We got an offer which we thought at this time was a good offer," Moyes said of a deal that reportedly resulted in a near €30 million loss on West Ham's club-record signing. "We didn't know if we would receive that offer later or at a time to suit us so that was a decision we had to make."

How Haller found form with Ajax

Haller has made hindsight on that particular "decision" unpleasant after resurrecting a career that some may have written off.

His journey in Amsterdam began with a bump in the road when the club forgot to add his name to their revised UEFA Europa League squad list. It has been the sole blemish on an otherwise stellar record which has seen him produce 24 goals and nine assists in 35 appearances.

"Sebastien arrived in Amsterdam in January and has integrated very well with the team," said Ajax sporting director Edwin van der Sar. "He scores and scores and scores!"

Unlike West Ham, the Dutch record titleholders had a ready-made team capable of playing to Haller's strengths. Their depth and movement out wide, coupled with the creative flair that always been demanded in Amsterdam, have allowed Haller to thrive in front of goal. 

A transfer to Dortmund coming?

On Tuesday, the French-born striker will put his prolific streak to the test against Dortmund, in what could be a shootout between two enterprising young sides as both look to preserve their unblemished records in Group C.

"In the Champions League, we will face Borussia Dortmund and the match between Haller and Haaland will certainly be fascinating," said van der Sar. Fascinating indeed as Haller is reportedly being viewed by BVB as a potential solution to the problems that will be caused by Haaland's inevitable departure.

When asked about the speculation by Sport Bild, Ajax coach Erik ten Hag admitted: "I don't know Dortmund's plans, but with Sebastien's class, I won't exclude the possibility that he is interesting for BVB. What I can say: He would be very expensive."

If Dortmund do sell Haaland, they shouldn't have too much trouble matching the price tag.