Muamba fell to the ground in the 41st minute with no players around him. The quarterfinal was immediately stopped, then abandoned.
Medics rushed onto the field with a defibrillator and treated the 23-year-old, pumping his chest for about six minutes of treatment.
Some players appeared to be praying as fans chanted his name between periods of complete silence at White Hart Lane.
After Muamba was carried off on a stretcher with an oxygen mask and with his chest still being pumped, all the players also left the field before referee Howard Webb abandoned the match.
Bolton manager Owen Coyle and forward Kevin Davies accompanied Muamba to a hospital. Bolton said there were no further details on his condition.
"Terrible what happened with Muamba during the game," Tottenham's Rafael van der Vaart wrote on Twitter. "We're all praying for him."
Muamba's Bolton teammate Stuart Holden, who was watching the game on television, tweeted: "Praying for you Fab."
"Waiting anxiously for updates from teammates," he added. "Fab is a fighter!"
Muamba was born in what was then called Zaire on April 6, 1988. His father left the country because of political turmoil and settled in England, and Muamba joined Arsenal's youth academy in 2002.
He made his debut at age 17 on Oct. 25, 2005, in the League Cup at Sunderland, and was loaned to Birmingham in the League Championship the following season. The loan was made permanent in May 2007, and he made his Premier League debut for Birmingham in 2007-08 before joining Bolton in June 2008.
"I seriously hope my best friend in football is OK. Stay strong bro please please stay strong," said Middlesbrough defender Justin Hoyte, who came through the Arsenal youth team with Muamba.
Muamba has been part of England's youth system and was a member of its team at last year's European Under-21 Championship, where he came on as a substitute against Ukraine and started against the Czech Republic.
"Our thoughts and prayers are with Fabrice Muamba and his family right now," the Football Association posted on its Twitter account. "A wonderful person."
Copyright 2012 by The Associated Press
