Kightly has been ruled out for the remainder of the season and McCarthy believes the 23-year-old's absence will create a greater incentive for his fringe players in the remaining games of the season.
"I would love Kights to be part of the promotion team and can understand players want to win it for him but I am sure they also want to win it for themselves and have done all season long," McCarthy told the Birmingham Mail.
"You have to be selfish to a point. If winning it for Kights adds a bit of incentive against Birmingham - fabulous.
"Someone has a chance and they can either dwell on the fact that Kights is out or accept it has happened and carry on.
"We can do nothing about it now. Someone else will now get a chance and we have plenty of players who can play in that position. We have to crack on."