The defender signed for Albion towards the end of August but is still waiting for clearance from the relevant authorities.
And even if it comes in time, Roberto Di Matteo will have to assess Jara's match fitness due to his exertions while on international duty with Chile in midweek.
The Baggies head coach will also check on fellow internationals Chris Brunt, Robert Koren, Marek Cech and Graham Dorrans.
Winger Brunt (calf) and strikers Chris Wood and Luke Moore (both ankle) should all be okay to feature in the matchday 18 having recovered from their respective injuries.
Long-term absentees James Morrison (heel), Neil Clement and Ishmael Miller (both knee) all remain sidelined and Di Matteo is refusing to put a timescale on their return.
Plymouth are set to be boosted by the return to fitness of experienced central midfielder Karl Duguid for the trip.
Duguid - who can also play in defence - missed the 3-1 home defeat by Sheffield Wednesday after suffering an ankle injury in the 2-1 defeat at Derby.
Right-back David McNamee also picked up an ankle injury against the Rams, but he too has recovered and is likely to return to Paul Sturrock's squad.
On-loan Cardiff defender Darcy Blake replaced McNamee against Wednesday.
Blake suffered a slight hamstring strain while on international duty but he is also expected to be fit for selection on Saturday.
Argyle are expected to recall Hungarian international central defender Krisztian Timar or start Benin international Reda Johnson in place of Marcel Seip, who was transfer listed this week for a "breach of discipline."
Sporting Life