An outbreak of the virus in the Rovers camp has affected several of the players and members of staff, with Allardyce himself suffering earlier this week.
Most are now fully recovered but Roberts has been seen by a doctor after showing symptoms of the illness and looks likely to miss Saturday's match against Manchester United.
"I'm okay now - I think we've only Jason Roberts," said Allardyce.
"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."
Samba still weakChristopher Samba is one player still feeling weak after contracting swine flu last week and Allardyce is not sure if he will be able to take part at Old Trafford.
"We've just got Chris Samba back, who seems to have been affected the most by the symptoms," explained Allardyce.
"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."
WorryAllardyce, who watched Tuesday night's clash with Peterborough from the stands 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."