Right-back Karl Duguid turned his ankle just before half-time in Saturday's 1-0 home defeat to West Brom and is ruled out, so his replacement, David McNamee, is set to keep his place.
Mariner handed a debut to new midfielder Damien Johnson alongside skipper Carl Fletcher, with youngster Luke Summerfield dropping to the bench.
He is set to stick with that pairing against the Royals, although new American striker Kenny Cooper could start in attack ahead of Rory Fallon.
Cooper was a second-half substitute against West Brom, but showed enough to suggest he could make a positive impact for Argyle.
Source: PA
Source: PA