The Bluebirds have lost five of their last six games and are on their worst run of the season.
But the club haven’t been in danger of the drop from the National League South - and the manager knows it’s been a mixed campaign.
Collier has spoken to the Gazette and Herald about what he expects in the last three weeks.
The club’s players have four games to prove themselves as he plans to freshen things up for 2019-20.
“There are four or five players, who have been absolutely outstanding and a credit to work with,” he said.
“Then there are another four or five who haven’t done enough, and we need to have conversations with them.
“We will have those conversations over the next few weeks, but players are running out of time to make their mark.
“The ball is in their court. We are down to limited numbers at the moment, so if players do get an opportunity, they need to grasp it with both hands and make sure they are in the forefront of my thinking for next season.”
They face tough games against Dartford, Chelmsford and Torquay and also play Gloucester City who will be fighting to stay up.