Previews: United keen to kill off Liverpool
Within hours of Liverpool losing 1-0 at Sunderland last week courtesy of a goal deflected in via a beach ball thrown on to the pitch by a fan, the Liverpool club shop's entire stock of the inflatables had sold out after a rash of internet orders.
Gleeful Man Utd fans, never slow to glory in the struggles of their north west rivals, are presumed to have been behind the sales surge and Anfield stewards will be primed to keep the balls at bay during Sunday's match.
But even if some Liverpool supporters will be suppressing a sly smile at the absurdity of it all, the prospect of a fifth defeat in a row and fifth in 10 Premier League games is certainly no laughing matter.
It would mark Liverpool's worst run for more than half a century and leave them 10 points behind United and potentially nine behind Chelsea, who host Blackburn Rovers on Saturday.
With the likes of Arsenal, Manchester City, Tottenham Hotspur, Aston Villa and Sunderland also above them, the chances of Liverpool somehow steaming through to take their first title in 20 years look remote and will surely be impossible if they lose again.
The club's fans are famed for the support they give their side and their manager but sections of the crowd booed the team off after Tuesday's Champions League defeat by Olympique Lyon, having also jeered Benitez after he replaced goalscorer Yossi Benayoun with Andriy Voronin late in the game.
Steven Gerrard, who lasted 25 minutes of the game after a premature comeback, Fernando Torres, Albert Riera and Glen Johnson are all struggling to make Sunday's game, piling the pressure on Benitez.
"I cannot remember an injury situation like this," he said.
"I have no idea what team I can put out against Manchester United until we have had the players tested and seen by the medical team."
United, in total contrast, followed their return to the top of the league last weekend with a 1-0 win at CSKA Moscow to put them in control of their Champions League group.
The long return trip will probably not do them any favours but any tiredness should be eradicated by the adrenalin rush produced by one of the most eagerly-awaited games of the domestic season.
Their chief injury concern is Wayne Rooney but they have shown they can win with or without the England striker.
Chelsea, beaten at Aston Villa last week, warmed up for the Blackburn game by hammering Atletico Madrid 4-0.
Third-placed Spurs will expect to maintain their push for a top-four finish at home to Stoke City while Arsenal are at West Ham United and Manchester City host Fulham.