The Australian striker is unsure about his future with the Lions after pondering a potential move to Scotland's Hibernian last week which forced Holloway to leave him out of their past two Championship matches.
McDonald missed the weekend's 3-0 loss at Reading and Tuesday's 1-1 draw with Sheffield Wednesday on Tuesday after exploring his options and will now have to toe the line if he wants back in Holloway's line-up.
"Scott and I have had some discussions," Holloway told News At Den of the former Celtic star.
"He needs to deal with how he feels and where he is in his mind.
"I haven't got any issue with him, we're getting on fantastically well. I never say never to anyone. But I've told him how I feel and I went without him on Tuesday night.
"If that helps him to do what I want, then there is no problem between us and I will have no issue with welcoming him back to the fold.
"But if he does what he thinks is right, and not what I think is right, then he won't be here, it is as simple as that."
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