Tuesday night in Paris was a reminder of what Liverpool are missing. Luis Diaz tore through the PSG defence like a man possessed, winning a penalty and scoring to keep Bayern Munich's Champions League hopes alive in a thrilling 5-4 first leg defeat.

For those Reds supporters still seething about his £65million departure last summer, it was salt in a wound that refuses to heal. Here was their former winger lighting up Europe's biggest stage whilst Liverpool continue to struggle for consistent quality down the left flank.

But before we all lose our heads in hindsight's perfect vision, let's remember the full story. Diaz had been open to leaving Anfield for some time. With Liverpool having already committed to new deals for Virgil van Dijk and Mohamed Salah, contract talks with the Colombian had stalled completely. When Bayern came calling with an offer that would net the Reds a significant profit on a player approaching his 29th birthday, the business case was clear.

Sound business decisions don't always make sound footballing ones though. That's the uncomfortable truth Liverpool are living with as they watch Diaz flourish in Bavaria. The hierarchy will undoubtedly be reflecting on how future situations might be handled differently.

What makes the fan outcry particularly interesting is the collective memory loss at play here. Less than two years ago, sections of the same support wanted Diaz gone, frustrated by what they saw as poor returns in goals and assists. Football supporters, eh? Fickle doesn't begin to cover it.

Credit where it's due though. Diaz's final season at Anfield was exceptional. Twenty goal contributions in 36 Premier League games as Liverpool secured their 20th title was elite level production. More telling was his versatility, spending over a third of that campaign operating as the central striker rather than his natural left-wing position.

If there's one quality Liverpool have missed most acutely since his departure, it's Diaz's ability to drive forward with the ball at pace. Whether relieving defensive pressure or sparking counter-attacks, he could get the Reds up the pitch in a way they've simply been unable to replicate this season. Both defence and attack have suffered as a consequence.

That deficiency will be front and centre of Liverpool's summer planning. With Mohamed Salah departing and Federico Chiesa potentially following him out the door, plus Hugo Ekitike facing a lengthy injury layoff, the forward line needs major surgery.

Seventeen-year-old Rio Ngumoha can expect more minutes next season, but Liverpool are sensibly reluctant to place too much burden on teenage shoulders. Cody Gakpo will remain important whether deployed left or centrally, but he lacks those natural attributes the Reds are crying out for.

Fresh faces are needed, hence the strong links with RB Leipzig's Yan Diomande amongst others being assessed. The recruitment team have their work cut out.

Tuesday's Parisian feast offered other painful reminders too. Khvicha Kvaratskhelia, long linked with Liverpool, has developed into one of the world's finest wingers. Michael Olise's dazzling display will have pushed his asking price beyond most clubs' reach.

Nearly a year after Diaz's departure, Liverpool still haven't found his replacement. That cannot continue into another season. The transfer window ahead will define whether the Reds can finally solve their left flank puzzle or continue paying the price for letting their Colombian magician slip away to Bavaria.