Wanderers have a small squad and although Ainsworth insists he likes working with fewer numbers as he feels it improves squad unity, it does put a strain on playing resources over the course of a season.
The manager admits leaving the likes of midfielders Jason Banton, Stephen McGinn and defender Danny Rowe on the bench for Saturday’s 3-0 win over York gives him options.
Midfielder Ryan Sellers, after recovering from a dead leg, was an 89th-minute substitute at the weekend and he will be looking to for more pitch time against the Cottagers.
Fulham have no fresh injury concerns for the trip.
Manager Kit Symons, who saw his side open their Sky Bet Championship campaign with a 1-1 draw at Cardiff on Saturday, will be without Luke Garbutt, Scott Parker (both ankle), George Williams (cruciate ligament) and Fernando Amorebieta (knee), who remain sidelined through injury.
Ryan Tunnicliffe, meanwhile, will serve the second game of his two-match ban.
The Cottagers progressed to the fourth round last season before they were knocked out by Derby.