LONDON (AP) -- Bolton player Fabrice Muamba was still fighting for his life in intensive care on Sunday night, remaining in critical condition a day after collapsing during a match because of a cardiac arrest.
The 23-year-old midfielder's heart only started beating on its own when he arrived at a London hospital on Saturday night from Tottenham's ground, medics said.
Amid an outpouring of global concern for Muamba's health -- from FIFA executives to players at rival clubs -- members of the Bolton management team, relatives and friends visited him at London Chest Hospital.
"God is in control," Muamba's fiancee, Shauna Magunda, posted on her Twitter account. "Please keep praying for fmuamba its really helping I can feel it."
About 24 hours after Muamba collapsed to the field during a game televised to a worldwide audience, Bolton said he remained anesthetized.
"Everybody is praying for Fabrice, which is very important, and that has been a real source of strength to the family," Bolton manager Owen Coyle said outside the hospital. "It's great to be talented at football but it is more important to be a genuinely nice man, and Fabrice is that. We certainly hope he comes through this.
"Our concern is Fabrice and Fabrice only, and that's what all our energy is going into -- hopefully a happy outcome."
Muamba collapsed near the midfield line in the 41st minute of an FA Cup quarterfinal at White Hart Lane, and paramedics immediately began trying to revive him.
"Fabrice received prolonged resuscitation at the ground and on route to the London Chest Hospital, where his heart eventually started working," Bolton said in a joint statement with the hospital on Sunday. "As is normal medical practice, Fabrice remains anesthetized in intensive care and will be for at least 24 hours."
That rapid treatment was available at White Hart Lane was the result of changes brought in following a serious head injury to Chelsea goalkeeper Petr Cech in 2006. Paramedics and an ambulance are now required at matches.
There was uncertainty about the causes of the cardiac arrest for Muamba, who was described by former Birmingham manager Steve Bruce as "one of the fittest players I have managed."
The Professional Footballers' Association said there are annual heart screenings for soccer players.
"While we have been able to pick up quite a number (of heart defects) and then been able to put them right, it is not always possible," PFA chief executive Gordon Taylor told The Associated Press. "This sometimes happens to young men and women who would be the last people you would think about having such a defect, and then suddenly it is found out."
Dr. Graham Stuart, a Football Association-accredited cardiologist, said detecting heart defects can be problematic.
"Usually in these cases the reason for this happening is something to do with a heart muscle problem or there is a weakness in the heart muscle," he said. "It could also be a primary arrhythmia disorder -- that is where there is an irregularity in the heart of the ionic channels."
Clive Clarke collapsed because of a cardiac arrest at halftime of a 2007 match while playing for Leicester at Nottingham Forest. He fully recovered, although he never played again.
"They know it was a cardiac arrest but don't know exactly what brought it on," Clarke told the BBC. "I have now got an internal defibrillator that was fitted while I was at hospital, which hopefully prevents my heart stopping again."
Bolton experienced a similar medical trauma in 2004 when retired Senegal forward Khalilou Fadiga collapsed on the field before a League Cup game, also against Tottenham. He returned to training 11 days after surgery to treat a heart problem that required an automatic defibrillator to be implanted, and he later returned to action.
Bolton chairman Phil Gartside urged fans around the world "to keep Fabrice in their prayers" in the hope of a similar recovery.
On Sunday, fans left flowers, Muamba shirts and scarves at Bolton's Reebok stadium, while there were public displays of support in grounds across Europe.
Former Bolton defender Gary Cahill celebrated scoring his first Chelsea goal in an FA Cup match against Leicester by unveiling a "Pray 4 Muamba" T-shirt. In the Spanish capital, Real Madrid players donned "Get well soon Muamba" tops before kickoff against Malaga.
FIFA President Sepp Blatter said on Twitter: "Shocked to hear about Fabrice Muamba. My thoughts are with him and his family, his club & loved ones at this difficult time."
As Muamba's teammates try to deal with the shock, their game against Aston Villa in the Premier League on Tuesday was postponed.
"I have worked with Fabrice as a player at Birmingham and he has always been a terrific lad, nothing other than the perfect professional," Villa manager Alex McLeish said. "He trained every day the way he went to play in games, full of intensity and enthusiasm. He is a manager's dream in terms of his commitment to the team ... the massive response throughout Europe and the world of football underlines how everybody has been touched by this tragic development."