Cairney, who made an instant impact after signing from Partick Thistle in the summer, has struggled in recent weeks and has not featured in the team for the last three games.
The arrival of Matt Done, on loan from Barnsley, and the recent form of 18-year-old Alex Harris has knocked the 25-year-old down the pecking order at Easter Road.
When asked about Cairney, Fenlon said: "When I can see him fitting in, to be honest. Like everyone else, Paul has to earn the right to play in the team, that goes for everyone not just him.
"I feel he has tapered off a little bit, but he still has a lot to offer. We have a lot of big games coming up.
"Paul has been part of the squad but I have left him out over the last few weeks and hopefully that will refocus him a little bit as well."