The physics of football state that when a large body hits a small body with great force, the large body will soon be standing over the small body. Similarly strenuous science also tells us that large bodies occupy more space than smaller bodies, and that two people cannot exist in the same space at the same time.

All of this is very important to the Buffalo Bills and their defense that’s been playing without one of its largest bodies and a 2010 Pro Bowler for the past three games. Kyle Williams is a vital piece of the Bills’ front seven, and he hasn’t appeared in a game since Week 5 because of a left foot injury. At first the hope was that three weeks of inactivity–a rest period that included Buffalo’s Week 7 bye–would be sufficient healing time.

The Bills will find out soon if that prognosis was correct, and they’re already bracing for bad news.

Williams was scheduled to have an MRI today, and he’ll then travel to Charlotte, North Carolina “tomorrow or the next day” to meet with foot specialist Dr. Robert Anderson, according to Bills head coach Chan Gailey. That’s when the future of Williams’ 2011 season will likely be known. He’s been working through an injury first suffered in training camp that became a nagging nuisance before finally shutting the 28-year-old down about a month ago.

Gailey wasn’t exactly brimming with optimism when asked about the Bills’ chances of getting their regular nose tackle back this year.

From WGR 550:

When asked if the injury is thought to be one that could jeopardize the remainder of Williams’ season, Gailey didn’t rule out anything.

“That is a possibility, I’m not going to say it’s not,” he said, lowering his voice in disappointment.

Williams is a duel threat, excelling against the run and pass. Last year he finished tied for second among nose tackles with 5.5 sacks, and he’s put the quarterback on the ground 9.5 times over the past two seasons.

He also had 77 tackles last year, plugging a hole up the middle and being one of the few reliable tacklers for a run defense that was routinely gashed in 2010 (169.6 yards per game). Williams signed a six-year contract extension near the conclusion of training camp worth $39 million with $17 million guaranteed, so there’s a hefty investment now spent on a player who hopefully isn’t dealing with a chronic injury.

While the Bills’ pass rush may be floundering without Williams (Buffalo’s 27 sacks places it in a tie for 27th, only five sacks above the last place Broncos), the run defense has actually been strengthened, partly due to the work of Williams’ replacement.

Rookie first-round pick Marcell Dareus has played nose tackle over the last two games, and has 2.5 sacks and nine tackles during that stretch. Although recent weak rushing opponents have definitely helped, Buffalo’s average rushing yards per game allowed has improved dramatically since Week 6 (91.3 yards) when compared to the first five games of 2011 (138.4).

UPDATE: It looks as though Williams is indeed done for the year.