The song - though to be on the band's forthcoming 'Mylo Xyloto' album - received a "hypnotic" reaction when the group performed it for the first time at their iTunes Festival show in London this July, despite vocalist Chris Martin only starting it a day before.
An entry on the band's Roadie42 blog said: "It's immense. I first heard it when the guys were sound-checking at the iTunes show. Apparently, Chris had started the song the previous night, so it was less than 24 hours old at that point.
"It was hypnotic in its simplicity, but devastatingly, achingly gorgeous. The final version has lost none of this and is a masterwork of restraint. It hasn't been crammed with a million ideas and embellishments.
"Every part is there simply to enhance the emotional impact. I can only predict floods of tears in every quarter."
The crew member compared how they perceive the song will be received to the impact the band's 2005 ballad 'Fix You', from their 'X&Y' album, had.
The roadie added: "It only took a couple of listens for that song to burn itself forever into the brain. Even on a first listen, the degree to which people would take it to their hearts was completely obvious."