Manchester United overcame Reading to book an FA Cup quarter-final berth at Old Trafford - but the 2-1 victory came at the cost after Phil Jones was forced off with a first-half injury.
Selected at right-back, Jones was hurt after attempting to tackle Reading skipper Jobi McAnuff and it was immediately obvious the former Blackburn man was in considerable pain.
Jones headed straight down the tunnel and it seems the man who helped subdue Cristiano Ronaldo in the first leg of United's Champions League last-16 tie with Real Madrid at the Bernabeu faces a battle to be fit for the return leg.
The third goal of Nani's disappointing season and Javier Hernandez's 15th strike of the campaign saw the hosts through, although McAnuff's late effort ensured the Red Devils were never able to relax.
On Friday, Ferguson had warned his players to "expect the unexpected" against Reading and the message appeared to have hit home in the opening stages as the hosts carved their opponents open at will.
A goalmouth scramble after just 90 seconds saw Hernandez's shot blocked, Danny Welbeck fluff the rebound and Antonio Valencia finally head straight at Adam Federici.
As it turned out, it was one of Federici's least taxing jobs.
The Reading goalkeeper was also forced to deny Welbeck and Ashley Young had a shot blocked before the visitors got into their stride, with Noel Hunt to the fore.
Hunt sustained a nasty cut following a collision with Nemanja Vidic that required two shirt changes, but also set the pattern for a bruising collision between the pair.
Vidic just edged it; one header out of his own six-yard box under severe pressure was particularly impressive, but it was Hunt who brought an excellent save out of David De Gea with a rasping 20-yard drive.
The sharpness had gone out of United's play by that point, although they should still have been in front after Federici pushed Tom Cleverley's long-range effort into Young's path.
It seemed the England man only had to hit the target. But Federici was able to scramble across to push the shot wide when really he should not have had chance to.
Funnily enough, Jones' departure, while potentially a major blow to Ferguson's plans for subduing Ronaldo next month, sparked the hosts into life.
Nani's third touch following his introduction as Jones's replacement saw him strike the far post with a fine volley, while his fourth was tipped over by Federici's flying save.
Hunt cleared a deflected Vidic header off the line, Federici saved from Anderson and Nani flashed a shot wide following the introduction of Robin van Persie.
Ferguson's obvious frustration at Reading slowing the game down extended to a message apparently being sent to the ball-boys to do their jobs with a little more speed.
There was one more save from Federici before the dam finally broke.
Nani's introduction had undoubtedly been significant and moments after his effort had been repelled, he strode onto Valencia's cross and supplied a deadly finish.
When Hernandez flashed home a near-post header on United's next attack, it appeared their work was complete.
Instead, McAnuff struck nine minutes from time to bring a familiar sense of nervousness to Old Trafford which only Andre Marriner's final whistle was able to ease.