The shocking contrast between Casemiro and Wataru Endo: Man Utd and Liverpool midfielders moving in opposite directions ahead of FA Cup quarter-final

United will go into the quarter-final on the back of a morale-boosting 2-0 Premier League win over Everton, but it was a game that did little to ease concerns over Casemiro's form.

The Brazilian had more touches than any other player on the pitch but 17 of his 70 passes failed to find their target. Of United's outfield players, only Scott McTominay had a worse completion rate (73 percent) than Casemiro (76 percent).

The worrying thing is that such carelessness in possession came as a little surprise to United fans, who have grown increasingly frustrated with the £70m ($90m) signing from Real Madrid.

It's not even that he looks nothing like the combative colossus that collected five Champions League winners' medals in nine years at the Santiago Bernabeu. He's even just a shadow of the player that had such an instantaneous and transformative effect on Erik ten Hag's team after his arrival from Madrid in the summer of 2022.

Put quite simply, United would not have secured a return to the Champions League had it not been for Casemiro.

According to the Daily Telegraph, after watching the 4-0 drubbing by Brentford at the start of the 2022-23 season, he had sent a text to his agent saying: "Tell them I'll fix it." And he did.

Casemiro proved precisely why he was regarded as the most destructive midfielder in football for the previous decade by immediately laying waste to Premier League opponents. He was United's human wrecking ball, ranking first among his team-mates for possession won, tackles won, duels won, aerials won, blocks and interceptions. This season has been a very different story, though.

Injury has obviously played a part in Casemiro's struggles, with the Selecao star sidelined from the middle of October to the turn of the year.

However, he was struggling horribly before then and some United supporters will tell you that the Brazilian was exhibiting signs of fatigue before the end of the 2022-23 campaign, in which he racked up more appearances (51) than he ever had over the course of a single season in Spain. Perhaps increasing injury issues and a dip in form were, thus, inevitable.

He's certainly not been helped by those around him, of course. Casemiro is not the only United player to underperform this season - far from it, in fact. Marcus Rashford and Bruno Fernandes have been nowhere near their best, while several key men have also been beset by fitness problems - as Ten Hag has been repeatedly at pains to point out.

The Dutchman hasn't done Casemiro any favours, either.

Ten Hag may have dismissed Jamie Carragher's claim that United have found themselves caught between two stools this season by employing both a high press and low block - but there's no doubt that Casemiro has at times looked confused, and consequently, frustrated.

This has manifested itself in Casemiro making far too many challenges that look as desperate as they are wild. Against Everton, the 32-year-old even had to be told to calm down by his teenage team-mate Kobbie Mainoo.

But such shows of petulance are arguably unsurprising. Firstly, this is not a man used to losing. Secondly, he has perhaps realised that he is locked in one particular battle that he simply cannot win.

Casemiro is younger than his two former midfield colleagues from Madrid, Luka Modric (38) and Toni Kroos (34), but it was inevitable that he would begin to wane before both, given the demands of his role.

He was arguably the most dynamic defensive midfielder in the world for the best part of a decade. As was the case with N'Golo Kante, who suffered an equally dramatic decline, it was only ever going to be a matter of time before playing such a draining position at a truly top team took its toll.

Endo, by contrast, is showing nothing like the same wear and tear, most probably because he hasn't played at the highest level for anywhere near the same amount of time.

Japan fans and Bundesliga followers will confirm that he's long been considered a terrific talent and an inspirational leader but he only arrived in Germany at 26 and has never played Champions League football. Indeed, he'd never even experienced continental competition outside of Asia until this season's Europa League.

In that sense, Klopp might be right about Endo. The thinking was that he was the stop-gap solution to Liverpool's No.6 problem but, based on the standard of his showings so far, he could, at the very least, end up staying at Anfield for the duration of his four-year contract.

Whereas Manchester United's new investors INEOS were immediately stunned by the scale of the investment the Glazers made in Casemiro, and are reportedly open to selling him to a Saudi Pro League club this summer, Fenway Sports Group's new CEO Michael Edwards is no doubt already acutely aware that in Endo Liverpool have landed another low-cost but high-quality player well worth holding onto for the foreseeable future.

Because at the very pinnacle of the profession, a player's longevity is often determined by miles on the clock rather than the age on the passport.