Bolton footballer Fabrice Muamba was "critically ill" in hospital on Saturday after collapsing suddenly during his team's abandoned FA Cup quarter-final with Tottenham.
The 23-year-old Kinshasa-born player was rushed to hospital after harrowing scenes towards the end of the first half at White Hart Lane, when the midfielder sank to the turf with no player near him.
Several paramedics were seen attempting to revive the player before he was stretchered off the field after 41 minutes with the scores at 1-1.
Muamba was wearing an oxygen mask and was flanked by a number of paramedics and Bolton medical staff as he left the pitch.
Referee Howard Webb called the players off the field before an announcement shortly afterwards that the game had been abandoned.
A joint statement from Bolton and the London Chest Hospital released at 9:30pm local time (2130 GMT) said Muamba was in intensive care.
"Bolton Wanderers can confirm that Fabrice Muamba has been admitted to The Heart Attack Centre at The London Chest Hospital where he is in a critically ill condition in intensive care," the statement said.
"No further information will be issued at this stage. The club and hospital request that the media and public respect the family's privacy at this time."
Earlier, players, fans and millions of television viewers had watched in anguish as paramedics treated Muamba on the ground at White Hart Lane.
Several players from both teams were in tears as the seriousness of the situation became apparent and fans sung Muamba's name as he was treated.
The stricken footballer's condition prompted an avalanche of concern on social-networking site Twitter.
Muamba's Bolton team-mate Stuart Holden tweeted: "Praying for you Fab. Hope he's OK. Thoughts with him and his family."
Commentating on ESPN, former Liverpool and England winger John Barnes said: "From the players' reaction on both sides it seemed that things were pretty serious."
Former England coach Kevin Keegan, also commentating on the match, added: "(Tottenham striker) Jermain Defoe seemed absolutely distraught.
"The fans are in a state of shock. I've never seen anything like that on a football pitch before. Our hearts go out to his family."
English football stars were quick to express their concern, with Manchester United defender Rio Ferdinand tweeting: "Come on Fabrice Muamba, praying for you."
Arsenal and England midfiedler Jack Wilshere, who played with Muamba during a loan spell at Bolton, added: "Hope Muamba is okay. Thoughts with him."
Spurs striker Defoe said: "Pray for fab god willing he will pull through #PrayForMuamba."
Middlesbrough defender Justin Hoyte -- a former youth team colleague of Muamba's at Arsenal -- posted: "I seriously hope my best friend in football is OK. Stay strong bro please please stay strong.
"God is with you remember that."
Tottenham midfielder Tom Huddlestone wrote: "Thoughts with Fab and his family. Feel sick watching this, puts football and everything else into perspective."
Bolton manager Owen Coyle and club captain Kevin Davies were reported to have gone to hospital to join Muamba, who moved to England from the Democratic Republic of Congo at the age of 11 after his father fled the war-torn country.