Louis van Gaal will have to field a makeshift defence against Sunderland on Saturday after confirming Marcos Rojo will not be fit for the match at Old Trafford.
Manchester United defender Rojo sat out Wednesday's Capital One Cup win over Ipswich because of a hamstring injury he suffered against Southampton last weekend.
With Paddy McNair also injured, Van Gaal was forced to play Ashley Young at left-back against Ipswich and the midfielder may play there again on Saturday.
When asked whether Rojo would be fit enough to return for the visit of Dick Advocaat's side, the United manager said: "No. The left-footed players, Luke Shaw and Marcos Rojo, are injured, so I have a problem."
Another option Van Gaal has is switching Matteo Darmian to left-back and bringing Antonio Valencia into the team on the opposite side of defence.
Daley Blind can also fill in at left-back, but Van Gaal is wedded to the idea of fielding a left-footed player at centre-back, so he will stay there this weekend despite the fact Phil Jones is now fit following his thrombosis problem.
"I have changed every player except a left-footed player so Daley Blind has played all the minutes (this season)," Van Gaal said.
"(Chris) Smalling had also played all the minutes and because of that I (substituted) him (against Ipswich) and brought Jones in.
"We have to spare players and Smalling and (Juan) Mata has played all the minutes, but I cannot spare Blind because all the left-footed players are injured."
Jones did not suffer any reaction to the problem that had caused him to miss the first nine games of the season.
"I said in advance to Phil about how many minutes he thought he could play... 20, 30? He thought more," Van Gaal added.
"It is not so easy to do that, but I asked him after the game if he felt fit and he said he did. He could easily have played more minutes so that's a good signal."
On recent form, Sunderland will cause United's defence little trouble on Saturday.
The Black Cats are winless and bottom of the table after six matches.
United beat Sunderland 2-0 at Old Trafford last year thanks to a Wayne Rooney brace.
The United captain has scored just two Premier League goals since that victory in February, but he found the net for the first time in domestic competition this season on Wednesday.
The England skipper cushioned Blind's long-range pass with his right foot before sweeping the ball past Ipswich stopper Bartosz Bialkowski with his left to put United ahead.
When asked whether it was a relief to see Rooney score, Van Gaal said: "No, no, because I have said that Wayne shall score sooner or later.
"It was a fantastic goal, the most beautiful goal of the evening."
Anthony Martial grabbed his fourth United goal after Andreas Pereira had doubled United's lead with a superb 20-yard free-kick.
Van Gaal praised Pereira's strike, but told the 19-year-old Brazilian he has work to do to make it into the first-team on a regular basis.
"He finished the game with a fantastic free-kick, he has the quality and that is why I let him take the free-kick," Van Gaal said of the teenager, who was making his full debut.
"He has quality but he is very young and he has to compete with players like Memphis Depay and Juan Mata."