At one point, Patrice Evra was the only fit senior defender.
Fletcher, Michael Carrick and rookie Ritchie De Laet constituted the three-man back-line at Fulham in December, when Evra was deployed as a wing-back.
Little wonder United slumped to a three-goal defeat, which has ultimately proved so costly in a battle with Chelsea that has gone down to the final day.
"Without those defensive injuries it could have been very different," Fletcher told MUTV.
"At one stage we had one fit defender in the squad. No team has been able to cope with that.
"We had three or four games in that position and ultimately it has cost us.
"If you are going to win the title in England you need a settled defence."
Having shrugged off the shattering disappointment of Liverpool's failure to put up any kind of resistance against Chelsea at Anfield last weekend, the equation for United now is simple.
Sir Alex Ferguson's men must try to ignore any whispers emerging from Stamford Bridge and maintain their focus on beating Stoke at Old Trafford on Sunday.
When that contest is over, they will then discover if Wigan have completed what would be ranked as one of the most stunning achievements since the Premier League began in 1992 by avoiding defeat against a team that has failed to win just twice on home soil this season.
"Although it doesn't look great for us, we just have to win and hope Chelsea drop points," said Fletcher.
"It is going to take a lot but we can only concentrate on ourselves. At least we are still in there fighting."
Should it become obvious the title has been lost, the worry is that the anti-Glazer demonstrations, which have been such a feature of the second half of the season, will become more powerful.
It is anticipated the Red Knights consortium will lodge a takeover bid in excess of £1billion before the World Cup begins in South Africa on June 11.
And some of the more militant United fans feel the Glazer family need to be given a nudge towards selling the club.