Mikel Merino
Spanish Under-21 international Mikel Merino has made nine appearances for Newcastle to date Stu Forster/Getty Images

Newcastle United look set to be without Jamaal Lascelles and Mikel Merino for their Premier League trip to Manchester United on 18 November, with worrying reports from the Spanish press suggesting that the latter faces between six to eight weeks on the sidelines through injury.

Influential midfielder Merino, who signed a permanent deal at St James' Park just three months after joining on an initial season-long loan from Borussia Dortmund, came off the bench to score a late winner on his last appearance against Crystal Palace but missed the subsequent back-to-back 1-0 defeats to Burnley and Bournemouth with a lower back issue.

Manager Rafael Benitez initially expected his fellow Spaniard, who was sent to visit a specialist, to be sidelined for at least a couple of weeks and hinted that his absence could be longer depending on how he responds to treatment.

Speaking at the Newcastle United Foundation's annual charity dinner this week, Benitez revealed that Merino was "getting better a little bit more every day" and that the club would discover next week if the injury would keep him out for longer than a fortnight.

However, Spanish sports daily Diario AS, as relayed by Sport Witness, now claim that the 21-year-old, ruled out of Spain's Under-21 European Championship qualifying double-header against Iceland and Slovakia, could be absent for up to two months with a problem in his vertebrae. However, it is unclear if such a timeline begins now or is backdated to when he first suffered the injury.

Newcastle skipper Lascelles, meanwhile, was forced off 10 minutes into the second half against Bournemouth after failing to recover from a left ankle blow sustained before the break. He left the stadium on crutches while wearing a protective boot.

Benitez is not confident that the centre-back will be fit to face United at Old Trafford, stating that his recovery process with the physios was progressing slowly and that they would have to wait a couple of days for the swelling to reduce to properly assess the state of the ankle.

"We will see with Jamaal," he added, per the Evening Chronicle. "It's very difficult for both of them [Lascelles and Merino] for Man United. If it was fine now, maybe you have one week of training but if not - even if he is fit, he will not be ready physically - it will be two weeks without training and you may not be physically ready for a game like that."

Benitez further revealed that defender Paul Dummett is now back in first-team training after an ankle injury that saw him limp out of the defeat to Tottenham Hotspur on the opening weekend of the season.

He also pointed to Christian Atsu's departure for international duty as a sign that he should be fine to play against Manchester United after a knock picked up last weekend, although Ghana revealed on Wednesday that the former Chelsea winger had withdrawn from a training session in Cape Coast due to a thigh complaint.

The Ghana Football Association (GFA) said he would continue to be assessed in advance of the Black Stars' final 2018 World Cup qualifier against Egypt on Sunday.