Centre-half Beckwith was sent off in last weekend's defeat at Bradford and serves a one-match suspension while Osman pulled a thigh muscle at Valley Parade and will miss out.
Manager Ian Sampson said: "Abdul Osman pulled his thigh against Bradford so that's probably the end of his season.
"We probably should have taken him off on Saturday but he picked up the injury with 15 minutes to go and we didn't have any subs left by that point."
Midfielder Luke Guttridge does return from a three-game ban of his own and is a ready-made replacement for Osman while Craig Hinton is likely to return in defence to replace Beckwith.
The Cobblers have no other injuries as they look for a win which could see them sneak into the play-offs if other results go their way.