Hibs began the day with an outside chance of making the top six ahead of the SPL split, but the visitors went down 3-0 at Celtic Park without ever really threatening to make a game of it.
And Fenlon was less than happy ahead of next week's Scottish Cup semi-final against Falkirk at Hampden.
He said: "I don't think there is too many who came off the park today who can have a moan if they are not in the team next week.
"It gives me a lot to think about because that performance is not good enough. We had three or four who had pass marks, the rest didn't do enough.
"It is a big week for people in training now. If they want to get into the semi-final team they are going to work tremendously hard to do that because I didn't see that from some of them.
"We didn't show enough commitment or have the belief that we could give ourselves a chance to get into the top six.
"There was maybe a bit of acceptance rather than a desire to give ourselves a fighting chance and that is more disappointing than anything."