Midfielder, Chaplow, was always unlikely to face the R's at Loftus Road because of an injury problem, but right-back Richardson's absence is a blow for under-fire boss Nigel Adkins.
It was hoped the defender would get a run-out in Monday's development squad but a recurrence of a thigh injury has now left him with no chance of featuring in the game.
However, forward Guly do Prado could be involved after being left out of the squad for last weekend's 1-1 draw with Swansea.
Adkins is looking forward to the game as his side bid for a first away win of the campaign against a QPR who are the only side below them in the table after an 11-match winless streak.
He said: "I feel stimulated and I am looking forward to the next game in the Barclays Premier League game, which is away to Queens Park Rangers.
"It's the next game in the journey that we're on. Every game that you look at has three points up for grabs. That's what we've got to go and do."