Coach Chan Gailey provided the encouraging update Thursday after Jackson made it through his second straight day of practice since spraining his right knee in a season-opening loss at the New York Jets on Sept. 9.
Barring a setback, Gailey said he expects Jackson to play Sunday.
"Fred worked and worked well today, and there didn't seem to be any residual effect negatively from yesterday," Gailey said.
Gailey then reiterated what he said Monday, by noting he was still very optimistic of Jackson's chances of playing.
Gailey was far more cautious when discussing Spiller's status after the running back hurt his left shoulder in a 24-14 win at Cleveland last weekend.
Spiller returned to practice on Thursday, but worked only on a limited basis.
"He did OK," Gailey said. "It looked like he was moving well. And it looked like all of his range of motion was there. So we'll see where it takes us. I don't know where it's going."
That makes Jackson's return all that more meaningful to Buffalo (2-1) and its run-based offense which faced the possibility of being down its two top rushers in preparing to face AFC East rival New England (1-2).
Jackson would only say, "I feel good," after making his way off the field and heading to the training room for treatment.
That was an improvement after Jackson complained of soreness and swelling in his knee before practice.
"It was a little more sore than expected, but not too much," Jackson had said. "I'm more disappointed in the way that it feels today. I still want to play."
Jackson added that he still requires clearance from team doctors before he can suit up on Sunday.
"In my mind I play," he said. "But it's not always just totally up to me. But I feel like I can play right now."
Cornerback Leodis McKelvin returned to practice after he missed Wednesday's session because of a groin injury.
Though the Bills haven't entirely ruled out Spiller, it's regarded that he has a better opportunity to return next week, when Buffalo travels to play San Francisco.
"Do I feel I can play? I don't know," Spiller said. "It's still early. I've still got a couple of days before that decision is made. I'm just going to continue to take it day by day."
Spiller got off to a hot start in taking over after Jackson was hurt. He entered last week's game leading the NFL in both yards rushing (292) and yards from scrimmage (364). The 2010 first-round draft pick is off to such a hot start that his 10.1 yards per carry is the highest total two games into a season -- and with a minimum 25 carries -- since Jim Brown averaged 11.3 yards in 1963.