Former Newcastle midfielder Cheick Tiote has died at the age of 30, after collapsing in training with Chinese club Beijing Enterprises.
Tiote ended a six-and-a-half-year stay on Tyneside in February by moving to China after finding first-team opportunities under manager Rafael Benitez limited.
Benitez led the tributes to Tiote on Monday, hailing the Ivorian's professionalism and dedication in the few months they worked together.
The Spaniard said on Newcastle's official website: "It is with great sadness that I have learned of Cheick's death.
"In all the time that I have known him, he was a true professional, dedicated and above all, a great man.
"Our hearts go out to his family and friends at such a sad time."
The player's spokesman Emanuele Palladino confirmed the news in a statement on Monday afternoon, saying: "It is with deep sadness that I confirm that my client Cheick Tiote sadly passed away earlier today after collapsing in training with his club Beijing Enterprises.
"We cannot say any more at the moment and we request that his family's privacy be respected at this difficult time.
"We ask for all your prayers."
A statement from Newcastle said: "We are devastated to have learnt of the tragic passing of Cheick Tiote at the age of just 30.
"The thoughts of everyone at Newcastle United are with Cheick's family, friends, teammates and everyone connected with the clubs he represented."
Former Newcastle captain Alan Shearer tweeted: "Devastating news of the death of Cheick Tiote. RIP."
Alan Pardew, Tiote's manager for much of his spell in England, expressed his deep sadness.
"I'm devastated to hear the news about my former player and friend Cheick Tiote," Pardew said in a statement, quoted by independent.ie.
"From the moment I arrived at Newcastle, Cheick was a wonderful presence around the dressing room and his performances on the field often defied belief."
He added: "None of us will ever forget that incredible day when our Newcastle team came from 4-0 down to draw an unbelievable Premier League game against Arsenal, with Cheick's incredible goal in the final moments of that game one of the iconic moments in Premier League history.
"I loved him. He's everything that you want in a Newcastle player.
"To hear the news that he has passed away at the age of 30 breaks my heart and my sympathies go out to all his family and friends who will be devastated by this news."
Tiote began his career with Belgian club Anderlecht in 2005 before switching to FC Twente, where he made 86 appearances and won the Eredivisie title under former England manager Steve McClaren in the 2009-10 season.
He moved to St James' Park in summer 2010 for around £3.5million and immediately made his presence felt as an uncompromising presence in the middle of the park.
In his first season alone, he collected 15 yellow cards and one red but endeared himself to fans for his tireless approach and his popularity soared when he scored the equaliser that earned Newcastle a 4-4 draw against Arsenal after they had trailed 4-0 at half-time.
That left-foot volley from just outside the area proved to be his only goal for the north-east club, although his performances alongside Yohan Cabaye in midfield helped steer Newcastle to fifth in the Premier League the following term.
He captained the side at the start of the 2013-14 campaign, but injuries and a loss of form hindered his progress for the rest of his time with the Magpies.
Tiote was often linked with a move away, but it was not until four months ago that he eventually departed to China League One club Beijing Enterprises, where he made 17 appearances before his death.
He also earned 52 caps for Ivory Coast, playing at the 2010 and 2014 World Cups, while helping his country to the 2012 African Nations Cup final, where they lost to Zambia.
Former Newcastle team-mates paid tribute on Twitter, with former Magpies goalkeeper Steve Harper writing: "Gutted to hear the awful news about my former teammate Cheik Tiote today. Thoughts with his friends and family."
Jonas Gutierrez posted: "Sad news. Always going to be remember our time together at #nufc RIP my friend."
Shay Given wrote: "Shocked & saddened to hear of the passing of Cheick Tiote, I pass on my condolences to his friends & family, way too young."
Newcastle goalkeeper Tim Krul said: "Deeply sad to hear the news about Cheick.. One of my favourite teammates.. My thoughts are with his family."
Siem de Jong said: "Terrible news, R.I.P. Tiote. Always enjoyed sitting next to you in the dressing room my friend," while Papiss Cisse added: "Goodnight brother, You will be missed. My heart goes out to his family. Gone too soon."