Skipper Parker was rested for the win at Huddersfield a fortnight ago following a hectic fixture schedule and striker McCormack missed out with a knee injury, but both are now fully fit.
Boss Kit Symons can also add midfielder Danny Guthrie to his squad after he joined on loan from Reading, and full-back Kostas Stafylidis returns after suspension.
But Lasse Vigen Christensen (hamstring) and George Williams (cruciate) are still out.
Brentford make the short trip along the Thames without Liam Moore after the England Under-21 defender was recalled from his loan spell by Leicester.
Manager Mark Warburton has in-turn recalled centre-half Jack O’Connell from his loan stint at Rochdale to fill the gap in his squad.
Midfielder Lewis Macleod has recovered from a hamstring injury but is short of match fitness and striker Scott Hogan is still battling back from cruciate ligament damage.
On-loan Everton youngster Chris Long will be available after extending his stay with the Bees for another month.
Sky Tickets are giving you the chance to experience live Championship football. Buy tickets here & get a free NOW TV Sky Sports Pass PLUS you could win Soccer AM tickets.