Guitarist Tom Morello's musical skills were truly tested during his recent live gigs with Bruce Springsteen and The E Street Band because The Boss would ask him to learn brand new songs less than two hours before showtime.

The Rage Against the MAChine frontman was recruited to join Springsteen's backing group on his current Australian tour as a stand-in for Steven Van Zandt, who had to sit out the trek to complete filming for his cult Tv show Lilyhammer.

Morello, who had previously made guest appearances with The E Street Band, admits the Born to Run hitmaker regularly switched up the setlist for the concerts Down Under, but he only alerted his fellow musicians to the song changes shortly before taking the stage each night.

The 48-year-old rocker also confesses he has struggled to match Springsteen's stamina as the 63 year old has no problem rocking out for four hours at a time.

Morello tells Rolling Stone magazine, "I learned about 50 songs in three months for the tour, and every night, 90 minutes 'til soundcheck, Bruce will text me with seven or eight songs we've never played before. And then during the show, he'll call up songs we've never even discussed - some I've never even heard!

"Our band plays very differently night to night. It's not a repetition, it's a renewal. If you're doing it right, that's how it feels. Every night, there's six to eight songs I have literally about a nanosecond to prepare for. But it's fun. Now that I know that's the gig, I'm like, 'Let's go!'... But it's been a really fun challenge."

And Morello insists he's been flattered to perform with one of the all-time rock legends.

He says, "It's been great. It's been really an honour being onstage with one of my favourite bands - one of the greatest live bands of all time. I've been to a lot of Bruce Springsteen shows, but I've never been to four consecutive ones. And every show isn't just a different show - it's a completely different experience."

Van Zandt is due to rejoin The Boss' Wrecking Ball tour at the end of April (13) in Oslo, Norway.