Boller also missed practice Wednesday, so the Rams are almost certain to go with rookie Keith Null for the second straight week.
"I'd say we'd probably have to lean that way," coach Steve Spagnuolo said. "Let's find out where Kyle is today and tomorrow."
Teammates expect Jackson to play. Jackson was at Rams Park for practice Wednesday, riding a stationary bicycle while rehabbing a lower back injury that's hindered him for several weeks, but Spagnuolo thought Jackson might have practiced Thursday except for the illness.
Jackson is second in the NFL with 1,279 yards rushing. Samkon Gado and fellow backup Kenneth Darby have combined for 132 yards on 26 carries, 51 of them coming on Darby's run off a fake punt last week.
"Steven has shown he can do well without practice and I anticipate he'll do very well this week," Gado said. "I'd be very surprised if he couldn't go."
Most of the Rams were back a day after the team canceled Thursday's workout due to an undisclosed number of swine flu cases. Among them were center Jason Brown, who confirmed he was diagnosed with swine flu.
"I felt horrible, like crap," Brown said. "I felt like passing out. It attacks you and it attacks you very hard and very fast. Luckily there are antiviral medications to help you get back on your feet very fast."
Also missing practice Friday because of flulike symptoms were wide receiver Brandon Gibson and defensive tackle Darell Scott. Spagnuolo said four other players were limited in practice for due to the illness - Brown, tight ends Billy Bajema and Daniel Fells, and Gado. He refused to say which players had swine flu or the overall number.
Brown believes he contracted swine flu on the flight to Nashville, Tenn., to play the Titans last Sunday. He said he felt fine, if a bit weakened, after practice.
"My body feels fresh," he said. "But going out there I was winded very fast."
"This league, this game, is about mentally and physically tough people," Spagnuolo said. "Even the teams that are 14-0, 13-0, it's a mental and physical challenge, and ours is no different.
"We had some adversity this week but we're out here and we're expected to focus and get ready to play a game."
Another player, defensive end Leonard Little, was questionable with an infected knee.
"Obviously when you have a game with multiple interceptions there's some bad throws and some decision-making that needs to get cleaned up," offensive coordinator Pat Shurmur said. "But he has the makings, skill and ability to be a quarterback in this league."
The Rams have lost 22 of 23 games and have been outscored 192-86 at home where they failed to sell out for the second straight home game. Defensive coordinator Ken Flajole said in 32 years of coaching he can't remember being sick during the season.
"And if I was, I guess I convinced myself I wasn't," Flajole added. "I haven't paid much attention to it, and I guess probably my daughters would tell me I'm stupid that way, but I just go on and do what I do.
"The work still continues."
Copyright 2009 by The Associated Press