Herden, a second five-eighth, has a problem with his thigh and did not play in the loss against Manawatu last Thursday while Mather, who has impressed at centre, was forced to leave the field at half-time against Manawatu with tightness in his hamstring.
Otago coach Steve Martin said Mather was probably out for two weeks with a pulled hamstring.
Herden damaged a thigh in the win over North Harbour and he was unlikely to play on Friday night.
Halfback Johnny Legg is still out with an ankle injury.
Otago may move Andrew Parata out to centre and bring Aaron Bancroft into second five-eighth.
Alternatively, it could bring in league convert Michael Witt into second five-eighth where he played for Otago B against Mid Canterbury on Saturday.
Other options are to have Ryan Shortland play at centre, but he appears more of a winger, while Glenn Dickson could play at second five-eighth. The side loses some bulk with the unavailability of both Mather and Herden.
Otago lost to Manawatu 19-12 but winning a bonus point, coupled with a couple of other results, meant it stayed in eighth position on the table.
Martin said Otago did create opportunities in the match against Manawatu but a loose pass or a wrong option ultimately cost his side. He felt Otago was denied a try at the end when Adam Thomson appeared to score but was ruled out by referee Vinny Munro.
He said Northland playing at home for the first time this season would be a tough proposition.
Northland had its first home game switched to North Harbour stadium because of ground conditions at Okara Park in Whangarei, but it has been given the all clear, and a big crowd is expected on Friday night.
Otago has only won one game out of four but has picked up bonus points in all its games. Northland has won two of its games, and sits one point above Otago in the table.
"I've been saying it for a while but this competition is very topsy-turvy. You have to be on top of your game. If you are off your game by even 5-10% and a couple of opportunities go begging then any side can tip you up."
