When Eddie Jones took over the England job after the 2015 Rugby World Cup fiasco - his stated goal was to win the 2019 version.
He promptly turned the fortunes of English rugby around delivering back-to-back 6 Nations Championships - including a Grand Slam in 2016.
However, consecutive losses to Scotland and France in this year's tournament sees Ireland arrive to Twickenham as champions with a round to spare.
Former Irish coach Eddie O'Sullivan was speaking at Off the Ball's Heineken Rugby Club Roadshow on Wednesday and feels a third loss in a row against Ireland this weekend could really put Jones' squad on the back foot with next years's global showpiece fast approaching.
"The bigger thing for me is I think England can't afford to lose this game and as Martin talked earlier about just having to win the game - a game they have to win because if they lose on Saturday it's their worst 6 Nations since 2006," he told Joe Molloy.
"The team have been regressing during the Championship in their performances. They have issues in their back row, in their midfield and the plan for winning the World Cup looks very shaky if they lose on Saturday."
"It's got to be a mental headset for England that this is a massive game for them. In some ways - it will define their year. If this goes south then the next time they really get to address it is in November.
"Nobody is going to worry too much about what happens in the summer - it's not the same resonance and it's a long time to stew over something like this. Like a Championship that everyone thought at the start it's going to come down to Ireland against England next Saturday but England aren't even close - it's over.
"No one predicted Ireland would go to Twickenham as champions and I think that trajectory that England are on - they've got to live with that for the next six months and the only way they can kind of get some lift out of that is to win on Saturday," he added.
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