Manager Sam Allardyce, who has suffered with the illness himself in the last few days, said that he and most of his squad had recovered after an outbreak in the camp last week but confirmed that Roberts was being seen by a doctor.
"I'm okay now - I think we've only Jason Roberts," Allardyce said.
"There was another player suffering with it earlier in the week and Jason looks like it now, so we've left him at home and sent the doctor out to see him.
"The symptoms look very much like the general swine flu symptoms, so we will obviously go and get a full check on him."
Allardyce revealed on Monday that three of his players had contracted swine flu.
One of those was thought to be David Dunn, who looked in good health when he came off the bench against Peterborough in the Carling Cup on Tuesday.
Another was Chris Samba, who Allardyce said was back in training but still feeling weak.
"We've just got Chris Samba back, who seems to have been affected the most by the symptoms," Allardyce said.
"He's been left pretty weak, I think he has lost about four or five kilos. It is an incredible amount of fluid he has lost.
"We'll have to check if he is strong enough to be capable of being selected for the squad on Saturday. We'll run him through training today and see where we go from there.
"(Pascal) Chimbonda is fit from injury, Vince Grella is back in training for us but it might be a bit too soon for him. The squad has strengthened from last week, which is very important when you are going to Old Trafford."
Allardyce, who watched Tuesday night's match from the stand for fear of passing the virus onto his players, admitted he had been worried at times about how ill he really was.
"It was just your normal feeling of flu symptoms really, nothing worse that than from my point of view I'm glad to say," he said.
"But when you get home and you hear on the news that somebody has died from it, you wonder what the situation is.
"There was something particularly wrong (with that person) when they caught the virus and obviously that contributed to the death.
"I was achy, sweaty and had headaches. But it was bed for a couple of days and I'm alright now."
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