Louis van Gaal has already described Wednesday night’s FA Cup quarter-final replay at West Ham as Manchester United’s “last chance of a title”, though after the debacle at Tottenham on Sunday it could also be fairly billed as a final opportunity for the Dutch manager to convince an increasingly sceptical public he is worth persevering with for another season.

It is probably an exaggeration to suggest an FA Cup exit would force Ed Woodward to bring Van Gaal's unhappy reign at Old Trafford to an early conclusion. Nothing the United executive vice-chairman has said or done so far marks him out as such a decisive man of action and the possibility still exists that he would be wary of creating a vacancy that supporters might clamour for José Mourinho to fill. Tottenham's Mauricio Pochettino is beginning to emerge as the ideal candidate anyway, though to attract the Argentinian Woodward and his board would have to convince him that what Van Gaal said last week remains true, that United will always be a bigger club and a safer bet than Spurs.

At the moment it does not look like that, and that is wholly connected to the way the two managers have gone about their jobs in the past two years. Pochettino has built a team from a collection of talented but hitherto disparate individuals, as Van Gaal himself admitted last week. Spurs have bought well, too, and skilfully integrated their newcomers into a settled side to achieve a remarkable consistency. They are title challengers on merit and but for Leicester’s exceptional season would probably be out in front by now.

United supporters can only look on enviously, for, even making allowances for the disruption of the David Moyes season and the fractured side the Dutchman inherited, Van Gaal has presided over two seasons of extraordinary stasis. Even that might be putting the matter too kindly, for the league table suggests United are going backwards under Van Gaal and the evidence in front of one's eyes makes it impossible to disagree.

Playing Ashley Young as a centre-forward at White Hart Lane might have been excusable early in Van Gaal's reign, when he was still unsure of each player's capabilities and feeling his way around to see if positional tweaks might pay dividends. Two years into his managerial tenure it seemed simply baffling, especially as Young had not been getting games of late, Anthony Martial was being used out wide and Marcus Rashford had been asked to make way at half-time. The previous week Van Gaal had responded to Ángel Di María's criticism of always being used in different positions by accusing players of never looking at their own performance.

United's attacking performance at Spurs spoke for itself. They failed to score for the 13th time in the league this season and once again registered only a single shot on target. Defensively, Van Gaal apparently had harsh words for Marcos Rojo about losing Toby Alderweireld for the second Spurs goal, though the Argentinian was playing at left-back rather than centre-half, while Daley Blind, more comfortable at full-back, was doing the opposite.

If it is true that a mutinous feeling is developing in the dressing room as well as on the terraces it would be understandable. United are plainly going nowhere under Van Gaal, and without any detectable sign of improvement – even the bonus of Rashford's discovery appears to have been squandered – talk of three-year plans and incremental progress is all too evidently just talk. Pochettino did not need three years to turn Spurs into title contenders, after all. He just improved what he had and was able to assimilate reinforcements that did not cost the earth. Dele Alli is probably the find of the season while Alderweireld at £12m might be the defensive bargain of the century, and both were already playing in England. United paid more than that for Matteo Darmian, not to mention Blind and Rojo.

Just a few weeks ago Van Gaal was talking of the difficulties of fighting on three fronts but now United’s season is down to one. One front, perhaps just one game. If United can reach a semi-final against Everton at least Van Gaal could point to some evidence of progress.

It is debatable whether even winning the FA Cup would preserve the manager for another season – while he would have his precious title and record of winning something in every country in which he has worked, the club are likely to take a much more cold-eyed look at the final league position – though progress in the competition would give the beleaguered manager something to cling to in the coming weeks.

Yet one other comfort that disappeared at White Hart Lane on Sunday was the notion that in spite of their overall inconsistencies, United could still beat the big teams. No such luck at Spurs, and West Ham are only a point behind United in the league, fresh from putting a huge dent in Arsenal's title ambitions through what Van Gaal called "the Andy Carroll show" at the weekend. "We have to recover quickly," the United manager said. "Everyone knows this is the last chance."

(Guardian service)