Dad-to-be Marler out of England team to play Italy
England flanker Chris Robshaw holds aloft the Triple Crown Trophy following the Six Nations International rugby Union match between England and Wales at Twickenham, West London on March 9, 2014 - by Glyn Kirk
Mako Vunipola came off the bench to start instead of loosehead prop Marler -- who was named in the original starting XV announced by coach Stuart Lancaster earlier on Thursday -- with Matt Mullan filling the bench place vacated by Vunipola.
England must beat Italy to have a chance of denying either Ireland or France, who play in Saturday's final match of the tournament in Paris, the title.
An England statement issued late Thursday said Marler was staying at home with his partner ahead of the "imminent" birth of their first child.
With British and Irish Lions star Alex Corbisiero still sidelined with a knee injury, fourth-choice prop Mullan now finds himself in the match-day 23.
"It is important that Joe is with his partner at this exciting time," said Lancaster. "Family must always come first and everyone in the squad wishes them well.
"We have prepared for being without Joe and we have no doubt Mako will slot straight in and perform, as will Matt Mullan should he get an opportunity.
"Matt played in the autumn internationals. There's no problem with him, he's been involved right throughout the campaign. He's a good player to come on."
England are in a three-way fight for the title with Ireland and France, who meet in Paris in Saturday's final match of a staggered last day schedule.
Lancaster's men will first need to win in Rome to give themselves any sort of chance and they will want to win well to claw back their 49-point points difference deficit on leaders Ireland ahead of kick-off at the Stade de France.
But while England have never lost to Italy, their last two matches have been hard-fought, one-score, encounters with Lancaster's men prevailing 19-15 in Rome two years ago and 18-11 at Twickenham in the return fixture last season.
"Winning is the priority. We went there two years ago and there were different conditions. It was very difficult," said Lancaster.
"Look at the Scotland game (against Italy), that was 21-20 (to Scotland).
"Italy beat France last year and Ireland also lost. Wales and Australia both struggled two years ago.
"It's not an easy place to go and get a lot of points. We know what's coming."
England might have been eyeing a Grand Slam but for a dramatic 26-24 loss to France in their tournament opener in Paris where they were denied by Gael Fickou's converted try in the closing minutes.
But they have bounced back with well-deserved wins over Scotland, Ireland and defending champions Wales to clinch the Triple Crown.
And now Lancaster wants his youthful side to sign off from the tournament in style.
"The character we've shown has been excellent throughout. The attitude and desire to improve has been exceptional," he said.
"But we have to back that up with a final performance that means we leave the Six Nations in a positive state of mind for the New Zealand tour."
Lancaster had previously announced one change to his match-day squad with fit-again centre Manu Tuilagi replacing Alex Goode on the bench.
Revised England team to play Italy in a Six Nations international at Rome's Stadio Olimpico on Saturday (1230GMT kick-off):
Mike Brown; Jack Nowell, Luther Burrell, Billy Twelvetrees, Jonny May; Owen Farrell, Danny Care; Ben Morgan, Chris Robshaw (capt), Tom Wood; Courtney Lawes, Joe Launchbury; David Wilson, Dylan Hartley, Mako Vunipola
Replacements: Tom Youngs, Matt Mullan, Henry Thomas, Dave Attwood, Tom Johnson, Lee Dickson, George Ford, Manu Tuilagi