Ki Sung-yueng has returned to Newcastle after his Asian Cup campaign was ended by a hamstring injury.
The 29-year-old midfielder picked up the problem in South Korea's opening game of the tournament against the Philippines and has since aggravated it in training.
A club statement said: "Ki Sung-yueng has returned to Newcastle United after a recurrence of a hamstring injury suffered on international duty with Korea Republic.
"He first picked up an injury during his country's opening game of the Asian Cup, against the Philippines on January 7, and was substituted.
"After suffering a recurrence in training, the 29-year-old has been recalled by the Magpies. He is now back on Tyneside, where his injury will be assessed by the club's medical staff."
Ki last played for the Magpies in a 0-0 Premier League draw with Fulham, and his absence could hardly have been worse-timed, with Jonjo Shelvey and Mohamed Diame also on the casualty list.
Manager Rafael Benitez was unhappy at how early his player was required to meet up with the South Korea squad and his mood will hardly have been improved by events since.
The Spaniard has been forced to turn in the absence of his experienced trio to 21-year-old academy graduate Sean Longstaff, and he has taken full advantage with a series of impressive displays, the latest of them in Saturday's precious 3-0 victory over Cardiff which lifted the club out of the bottom three.
Just weeks after team-mate Matt Ritchie suggested there was a lack of belief within the club and Ayoze Perez spoke of "something wrong" at St James' Park, Longstaff is adamant the Magpies have what it will take to complete a second successive survival mission, and feels an FA Cup fourth-round victory over Watford this weekend will only help.
He said: "There's a lot of tired legs in there and a few bumps and bruises that need to be fixed, but, judging by the Cardiff game, everybody is up for the fight.
"Everybody will be raring to go again on Saturday. It's a good chance to progress in the FA Cup. Winning breeds confidence and it doesn't matter which competition it is.
"We won't get ahead of ourselves as there are tough games coming up. It is about building confidence and everybody will focus this week and look forward to it."
Benitez's men, who have won only two of their last 10 league games, face another difficult run of fixtures after the cup tie with Manchester City, Tottenham and in-form Wolves waiting in the wings ahead of potential key home clashes with Huddersfield and Burnley.
The manager is desperate to strengthen his squad during what remains of the January transfer window, with owner Mike Ashley having all but given up hope of offloading the club.
However, Longstaff's emergence from the ranks has given the Spaniard a boost in recent weeks.
The North Shields-born player made his home league debut against the Bluebirds and was thrilled to do so in such a potentially significant game.
He said: "It is hard to put it into words. It is unbelievable, but it is made all the sweeter by the win."
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