Louis van Gaal's selection problems deepened on Thursday after it emerged Manchester United striker Radamel Falcao will be out for at least a fortnight because of a new injury.
Falcao has had a difficult start to life at the club since his dramatic deadline-day loan move from Monaco.
The 28-year-old, who is among the top earners at Old Trafford, has scored only one goal so far and he is yet to play 90 minutes for the Red Devils.
Falcao has not played for United for a month because of a calf problem and he has now suffered another setback, the club confirmed on Thursday afternoon.
"Van Gaal tells #MUTV that @Falcao "has a new injury" and is at least two weeks away from a first-team return. #mufc," a post from the United's official Twitter account read.
"I am getting better, I feel well and I hope to come back to the pitch soon," Falcao told United's website.
"It is disappointing that I can't play but I have to be calm and recover because that is important to help the team when I return to the games."
The Colombian frontman said reports that he was struggling for fitness because of a knee injury he suffered last season were "pure speculation".
Even if Falcao had been fit, Van Gaal would still be facing a severe shortage of players for Saturday's crucial match against Arsenal.
The Dutchman could be without seven players after a damaging international break.
The biggest casualty was midfielder Daley Blind, who came off in the 20th minute of Holland's 6-0 win over Latvia with a knee injury.
Van Gaal said initial tests on the player's left knee proved inconclusive and he will undergo another scan the week after next to determine how long he would be out for.
The United boss said: "He has a brace on his knee and 10 days' rest and then we have to make another scan and then we can say more about his injury.
"It is not so bad as the doctor thought after the match but it shall be a long story, I believe, but not six months or something like that.
Blind was one of five United players injured on international duty. Luke Shaw felt a tight hamstring and groin while away with England.
"Shaw is a question mark," Van Gaal added.
Michael Carrick also suffered a groin problem on international duty, and he will be assessed before Van Gaal decides whether to include the player in the squad for the game at the Emirates.
"I have to wait for how he reacts in training, but I expect that he is also ready to play," Van Gaal said.
There was better news about Angel di Maria and David de Gea, who suffered foot and finger injuries while away with Argentina and Spain respectively.
"Di Maria has trained today normally so I don't think that is a question mark," Van Gaal said.
"David De Gea is good, no problem."
Van Gaal's squad was already hit by injuries to key players before the international break.
Phil Jones, Marcos Rojo, Jonny Evans, Rafael and Radamel Falcao all missed the 1-0 win over Crystal Palace two weeks ago, and it looks like they will miss Saturday's game against the Gunners too.
When asked whether any player who missed the Palace match was available for this weekend, Van Gaal seemed to suggest it would be highly unlikely.
"It's difficult to say if anyone is back because we have to wait for tomorrow's training session to decide if players are coming back," he said.
"But the players are not coming back in the squad - that's a different thing. My philosophy is that you have to train at least one week with the squad, but better two."
Danny Welbeck will face his boyhood club for the first time on Saturday since his £16million move.
Welbeck has scored 10 goals for Arsenal and England since leaving Old Trafford.
Van Gaal, who said in September that he sold Welbeck because of his poor scoring record, thinks the 23-year-old is benefittng from an extended run of first-team matches at his new club.
"I think that a player always who is playing mostly fixed in a team, he develops always better," he said.
"So he takes all the benefit that he plays every week. That was a question mark with Manchester United. So it's very good to see him doing what I thought."