Former Newcastle United manager Rafael Benitez remains a popular figure among many at St James' Park following his solid spell in charge of the club in the recent past, although one thing for which supporters won't thank the Spaniard is his decision to allow compatriot Mikel Merino to depart four years ago.

The promising midfielder had arrived on Tyneside on an initial loan deal from Borussia Dortmund in the summer of 2017, with that temporary move quickly made permanent just a matter of months into his time in England.

The Spaniard had made a fine start with Newcastle and was lauded for his composed displays in the centre of the park, having notably been compared by Benitez to former Liverpool and Real Madrid star Xabi Alonso.

That strong beginning was somewhat disrupted by injury in the second half of the 2017/18 season, with the 11-cap gem eventually going on to make just 25 appearances in all competitions, scoring once and laying on only one assist.

After a frustrating yet promising debut season with the Magpies, it then came as something of a surprise that the 6 foot 3 playmaker moved on at the end of that campaign, having been snapped up by La Liga outfit Real Sociedad.

According to reports at the time, the San Sebastian club had activated a buyout clause of just £10m in the player's contract to prise him away from the Premier League side, with the midfield maestro later admitting that the chance to return home had been too good to turn down.

Quite why Benitez and co sanctioned a release clause in his deal - particularly at a relatively low value - truly beggars belief, with Merino having since gone on to prove just what a stellar asset he is during his time in San Sebastian.

The £45m-rated ace has gone from strength to strength over the past four years, having notably been lauded as the "best player in La Liga" by coach Imanol Alguacil for his form of late.

The £65k-per-week genius - who has also been dubbed a "master" by one source - has racked up 159 appearances in all competitions since his arrival in 2018, scoring 16 goals and providing 17 assists from his midfield berth.

A defensive-minded player who boasts real quality in possession, the 26-year-old ranks in the top 3% for aerial duels won among those in his position across Europe's top five leagues, while he also ranks in the top 17% for progressive passes, showcasing his forward-thinking approach.

His talents were most recently on show in the win over Manchester United at Old Trafford on Thursday, with the one-time Osasuna man notably registering six interceptions in that 1-0 victory, with his SofaScore match rating of 7.3 bettered only by team-mate Alex Remiro among those involved on the night.

Such is his quality, the Spain international had even been tipped for a move to Manchester City earlier this year, with reports having suggested that Pep Guardiola's side were willing to meet his £50m release clause.

That valuation is a marker of just what a dismal mistake it was for Benitez to allow the midfielder to depart, with current Newcastle boss Eddie Howe likely to have loved the chance to work with such an undoubted talent.