Forest were held at second-placed Bristol City on Saturday, and Calderwood concedes that top spot is now beyind his side.
"Any victory Scunthorpe secure in their next three games puts them almost out of sight," he said.
But although Calderwood has chalked off hopes of the title, he is not giving up the chase for second spot - and the automatic promotion to the Championship that comes with it.
"City had better set their sights on overtaking Scunthorpe because we certainly feel we can still catch them," he declared.
"They were brilliant between going behind and half-time on Saturday. We were really stretched, but defended well and deserved something for our efforts."