Cotterill, who has the smallest squad in the Championship to work with, has seen his tiring side take just one point from their last four matches.
They host promotion-chasing Swansea on Saturday with little to play for themselves, sat as they are in mid-table.
But Cotterill is calling for one final push to end a gruelling season on a high.
"We've got four games left. We have got to try to keep 11 players on the pitch and do our best in those games," he said.
"We need to make sure we get back up for those."