JP is still recovering from the rib bruising that forced him off during the Heineken Cup match against Northampton Saints at Franklin's Gardens last Friday. Sean misses out with a calf strain.
Both players are expected to be fit for selection for Glasgow's league match against Neath-Swansea Ospreys at Hughenden on 29 January.
Sean's younger brother, Rory, is back in the frame for the Newport match on Saturday. He was not eligible for Glasgow’s European matches.