The club's most successful captain readily accepts that is the tag Super League's champions of the last three years will be tarnished with unless they quickly produce a distinct turnaround in form.
Whether that is even possible given the inconsistencies of their most troubled season of recent times remains to be seen but redemption can begin in their qualifying play-off at Wigan tomorrow evening.
Leeds had only finished outside the top two once in the last seven seasons yet needed a final-day victory at Hull FC a week ago to finally clinch fourth spot.
However, now that is done, Sinfield admits his side will attempt to start the play-off series as a fresh slate, forgetting all that has gone before including the bitter Challenge Cup final loss against Warrington and some turgid Super League performances.
But can such a transformation be made in such a short time with all the issues that have hampered them so far being rectified for the business end of the campaign?
"That is the challenge for us all," Sinfield told the Yorkshire Post. "I don't feel that at any part of our season we've been at our best.
"We've run at 50, 60 and maybe 70 per cent for the majority of the year.
"In many ways, now it's pretty scary; if we can raise our performance we know what a threat we can be but it is getting us to transfer what we're doing on the training field into the game.
"That's probably been the difficult aspect since the start.
"When you look at our squad we've probably got the best we've had since I've been here but unless we go out and perform we'll end up being under-achievers. That's what we are at the moment."
Wigan have claimed the League Leaders Shield following a thoroughly comprehensive assault on the competition but, until last week's win over doomed Bradford, had lost three of their last four games at DW Stadium which should offer Leeds encouragement.
England international Sinfield still rates the fixture "as tough as they come" but, on the back of a victory at Hull which not only guaranteed them the security of two play-off games but also acted as a massive morale-boosting exercise, there is hope their champion class will finally materialise.
He concedes being demoralised by Warrington a week earlier, when the Yorkshiremen truly thought their 11-year wait for Challenge Cup success would finally end.
"It was really important to put to bed and get some closure from the cup final," explained Sinfield, crushed by his third loss in the famous competition.
"I've lost big games before but that was really difficult to cope with because of how we lost.
"If you play your best but get beaten by the better side it is easier to take but to be a million miles from how we should have played, like we were, that hurts the most. I don't think we'll ever get over it completely but it was crucial we won at Hull."
They only managed to edge victory, despite their hosts being down to 12 men for 70 minutes, but there were fleeting signs that the fluent Leeds of old could be re-emerging.
"Everyone thought with (Lee) Radford getting sent off we'd rip them up but we had to really start to build things right from the bottom and get some confidence again," said Sinfield, who turns 30 tomorrow.
"We were facing a very, very committed Hull side but I thought we threw the ball around pretty well towards the end and that helped rid some of those demons."
Danny McGuire proved the difference, his fleet-footed genius producing two tries, setting up a thrilling contest against Wigan's Sam Tomkins, who nudged the Leeds man out of the England jersey last season.
"He's been outstanding this year and probably without him doing some of the things he has done we wouldn't have got into fourth," said McGuire's captain. "What happened at the end of the Four Nations really fired him up and he's been our best player by a mile."
Leeds, still weakened by the loss of Jamie Peacock, Jamie Jones-Buchanan and Luke Burgess, will not be able to solely rely on McGuire's brilliance tomorrow though given the imposing nature of this current Wigan side.
But Sinfield insisted: "The beauty of it is we've still got everything to play for.
"It might be new to us starting in fourth but we're still in a great position and Super League is up for grabs. We know what it takes to get to Old Trafford.
"Nobody's expecting us to win the Grand Final – no one is expecting us to win at Wigan – and we'll be going in as underdogs but the challenge is, come October 2, to be champions again."