There is no player on the New England Patriots that can replace what running back Dion Lewis brings to this offense. No player offers the infuriating size and quickness, paired with an abnormal amount of strength.
And yet the injury to Lewis is balancing between devastating (out for the season) and simply sever (out for a month and a half) and so the Patriots will have to adjust and find a way to replace Lewis in the offense.
There's already an example of the Patriots approach with Lewis on the sideline as the back missed the week 7 game against the New York Jets with an abdominal injury. In that case, the Patriots used 2014 4th round running back James White. White has been a healthy scratch in favor of Brandon Bolden because the former doesn't offer any special teams ability, while Bolden is serviceable on offense in case of an injury.
White is not Lewis. He doesn't offer the same power as Lewis while running the ball and his center of gravity is higher when he makes his cuts, leaving White open for hits. White is a good receiver out of the backfield and he can make defenders miss. He's also viable in blitz pick-up and, sure, he can run out of the draw play.
The Patriots offensive strategy won't have to change with White in the line-up, but its effectiveness will drop- and that's not even including the injuries to the offensive line.
Other than White, the Patriots could use Bolden (did you know that Bolden is only 25-years old?). Bolden flashed his route running against Washington with a gorgeous grab in the end zone and he has historically filled in when Shane Vereen was injured.
LeGarrette Blount could possibly take on a larger role, but he won't be asked to act like Lewis.
If the Patriots were to look at players currently on the street, here are some names of interest:
Travaris Cadet: the player that spent the entire offseason and the first month of the season with the Patriots remains a free agent. He is exactly what the Patriots would look for in a possible wild card out of the backfield since he's considered to have "wide receiver-like ability" running routes. He's not a polished runner or pass blocker, which is why the Patriots kept both Lewis and White over him, but he makes a lot of sense. Also adds special teams value.
Dri Archer: a 5'8, 180 lbs 2014 3rd round pick out of Kent State with blazing 4.26 speed would be an ideal match. Archer picked up 1,990 yards from scrimmage as a junior and is a threat as both a runner and a receiver. He is also a top tier kick returner. Archer won't break the tackles that Lewis was able to, but watch this and this. Get the ball in his hands and defenders won't be able to touch him. The Steelers just cut him this past week.
LaMichael James: this 5'8, 195 lbs rusher with 4.45 speed was one of the most productive runners in college history, posting 1,714 yards as a rookie at Oregon, followed by 1,939 and 2,015 yards. James never cracked the field for the 49ers after being selected in the 2nd round of the 2012 draft, getting stuck behind Frank Gore and Kendall Hunter on the depth chart, but he's capable. He spent the offseason with the Dolphins and he was responsible for tipping the scales against the Patriots miracle comeback against the 49ers in 2012.