Cobblers will have to keep a close watch on the 24-year-old South African striker, scorer of five goals in five games for Lincoln during his first month on loan at Sincil Bank.
Parent club Leeds United have agreed to extend Somma's stay until the end of the season although a 24-hour recall is in place.
The Imps have moved away from the relegation zone in League Two of late, Chris Sutton's side are currently unbeaten in their last five games.
They were beaten 1-0 at Sixfields in October in the reverse fixture of Saturday's clash.