It has not been an easy season for Roberto Firmino.

In truth, it has not been an easy couple of seasons. Ever since he was forced off injury in the first leg of the Champions League semi-finals against Barcelona in May 2019, he has endured something of a rollercoaster ride at Liverpool.

There have been highs and there have been purple patches in front of goal. And, of course, he's won the Premier League, Champions League, European Super Cup and FIFA Club World Cup.

But the shouts from his critics continue to get louder as the Brazilian is belittled for his decreasing goal return.

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Firmino is not your traditional centre-forward. He started his career as a defender before finding a new role.

And even when first rocking up in Europe at Hoffenheim, he was used as a midfielder.

But a 22-goal 2013/14 campaign with the Bundesliga outfit opened Jurgen Klopp 's eyes to the now 29-year-old's abilities.

Capable of playing as a 'false 9' in attack, the German initially turned to Firmino to fulfil such a role following their own moves to Anfield within months of each other in 2015.

And after recording double figures in each of his first four seasons on Merseyside, including a career-best 27 in 2017/18, the Brazilian shed the 'false' tag as he became Liverpool's central striker.

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However, after scoring nine Premier League goals last season and boasting just six goals this season, Firmino's role in Klopp's starting XI is under more scrutiny than ever before.

At times he has been dropped, with summer signing Diogo Jota taking his place, and there have been calls for Liverpool to sign a replacement for him this summer.

But, in partnership with Adidas, Firmino has issued a defiant message to his critics on social media.

In a paid partnership with the German sportswear company, the Brazilian has posted an advert on his Instagram profile with an image of just his eyes with the accompanying message: "Where some see a scoring striker, I see the possibilities of reinventing the position."

Adidas' slogan of 'Impossible is Nothing' is also on the image, with Firmino writing the same message along with #MadePossibleWithAdidas as the accompanying caption.

While just an advert, it doesn't make the sentiment any less true.

Whether his decline this season is the just as a result of the difficult circumstances the Reds find themselves competing in or something more long-term remains to be seen.

And while Liverpool will one day replace the Brazilian, his importance under Klopp over the years has been second to none.

Firmino might not be a traditional scoring striker, but he has certainly reinvented the position at Liverpool.