"Robbo is still part of our plans, but other players are ahead of him now," Grayson told BBC Radio Leeds.
"He still has an opportunity to play his part this season. But he's been bypassed by other players and that happens in football."
Another player to miss out on Tuesday's win at Tranmere Rovers was injured loanee defender Shane Lowry.
Grayson explained: "He has gone back to Aston Villa to get more treatment and some scans. So we'll have to see what happens with those. It's disappointing to lose him again.
"His loan expires at the weekend, but we do have the option to extend that. But it all depends on his injury as to whether he can come back here or not.
"I haven't needed to move into the loan market again because we've got players coming back from injury.
"In the last few weeks we've had four or five key players out, but now most are coming back, so the squad is looking healthy.
"If the right players come along that I feel we need I'm sure the chairman will back me to get them. But I'm very happy with the squad I've got at the moment."
Source: BBC Sport
Source: BBC Sport