Of all Everton’s failed summer transfer recruits, it is Michael Keane who has been the biggest disappointment.

Wayne Rooney’s return to the blue half of Liverpool was laden with sentimentality as much as it was sensibility, and while the 32-year-old is Everton’s top scorer with 11 in all competitions, his performances have largely been of a player leaning towards semi-retirement, little surprise given his stark decline over the last two years.

Sandro Ramírez and Davy Klaassen arrived at Goodison Park with an air of unknown mystique but expectations were tempered as they had never played outside of Spain and the Netherlands, so their inability to make an impact in such a short space of time can be put down to an ambitious and ill-conceived experiment.

In the case of Keane, however, he was not only a proven commodity, as an emerging centre-back yet to hit his ceiling after a breakout season for Burnley, but also, at 24, was ready to kick on to the next level, freshen up Everton’s ageing defence and prove its new cornerstone.

Except the kick has been more a succession of stumbles, with Keane looking a shadow of his Burnley self and instead of bringing stability, he’s been a fundamental part of their overall fragility.

Symbolically, and to compound the now 25-year-old’s regression, Gareth Southgate’s most recent England squad contained his replacement at Burnley, James Tarkowski, with Keane omitted altogether.

A Clarets’ defence which has simply swapped Tarkowski for Keane and banked £25million, lies fourth in the Premier League in goals conceded (26), with an 11th-best in expected goals against (xGA) of 41.58. By contrast, an Everton defence in which Keane has started 22 of 31 games is 16th in goals conceded (50) and 18th in xGA (48.57).

That gives considerable rise to the claim that Keane was merely a beneficiary of Sean Dyche’s impressive defensive system and/or thatBen Mee was really the superior centre-back in claret and blue during the 2016/17 season.

It’s worth noting that Burnley remain something of a statistical anomaly, over-performing in a variety of metrics and Keane’s individual defensive stats in the Premier League haven’t altered a great deal: 0.8 tackles per game last term against one this season; 1.3 blocks for Burnley compared with one in blue; 1.8 versus 1.9 in interceptions; 7.4 clearances against 6.5; 65.15 per cent of aerial duels won versus 57.57 per cent.

So, apart from getting beaten in the air a little more, Keane has been doing largely similar things for Everton as he was at Burnley, yet has looked considerably worse.

However, putting aside individual defensive stats as a definitive indicator of performance, it’s a slightly unfair and inaccurate comparison to make for some major reasons which provide the former Manchester United academy player a degree of mitigation for his troublesome campaign.

In Keane’s case, context and character are everything.

He's already played under three different managers, in Ronald Koeman, David Unsworth and Sam Allardyce, who have differing approaches to the game and, in a new job in a new city and with pressure he’s not been used to, Keane has had little time to adapt.

He’s has been removed from the familiarity of a club he made 108 appearances for, under the same manager, with a settled structure and culture to Everton, undergoing a major facelift in playing personnel and then mid-season transformation in the dugout.

Change that has also led to a rotating cast with 20 different centre-back and full-back combinations used in the Premier League, across back threes, fours and fives.

The most common? Jonjoe Kenny, Ashley Williams, Mason Holgate and Cuco Martina, used by Unsworth and Allardyce a combined six times. To emphasise the chaos, it will be a surprise if any of that quartet are in the XI against Manchester City tomorrow.

Compare and contrast with the familiarity of starting every week in a four-man defence alongside Mee, Stephen Ward and Matt Lowton.

The alarming form of Ashley Williams has also played a role. The Welsh captain has looked every one of his 33 years, lacking concentration and cumbersome on the turn, often leaving Keane exposed and uncertain. As the senior partner he should be the one guiding Keane’s integration. That clearly hasn’t happened.

Granted, Keane should have the ability to perform in spite of his team-mate’s failings but centre-back partnerships are symbiotic; when one individual struggles it tends to have a contagious effect.

There is also the issue of Keane’s health, as a foot infection saw him miss clutches of games through December and January, and it’s unclear whether he’s been 100 per cent at any stage.

But hope springs eternal, as performances of late, 2-1 defeat at Burnley aside, have given rise to optimism that Keane could play his way back into form.

In three of the last four matches he’s started, Everton have kept the opposition xGA to below 1.0, and he’s certainly looked more confident and assured with Phil Jagielka in a traditional four-man defence, securing back-to-back wins against Brighton & Hove Albion and Stoke City in their last two games.

It’s Jagielka who has provided the best insight into why Keane has struggled to be the dominating and assured presence at the back that £25million appeared to buy last summer.

Jagielka told Everton’s official website last week: “He is a quiet lad and I have openly said, ‘shout at me, shout at someone else, no one is taking anything personally, we need to know where everyone is,’ and I think he has that in him.

“At the start of his career here he had a few difficult periods so it was probably natural to go into your shell a little bit. But I am encouraging him to be himself and be a boss at the back – whether you are a loud person on or off the pitch, when you are on the pitch you need to pass information.”

The onus is on Keane to become that “boss” Jagielka believes he can be. With Manchester City at Goodison on Saturday, it provides a better opportunity than Brighton or Stoke to see not only his individual progression but also the dynamic with Jagielka, after two weeks of work together on the training ground.

As for England, he has seven league games to get back in Southgate’s good books. It is a distinct possibility with centre-back stocks not exactly teeming with quality ahead of Russia 2018.

However, even if Keane ends the season strongly, what it’s told us is flexibility is not one of his great strength, whether with managers, tactics or team-mates. And with Southgate’s recent squads hinting at his desire for malleable players who can adapt quickly to different systems and scenarios, the signs don’t look overly encouraging.

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