Leeds have made an impressive start to the campaign, and currently lead the way in the second tier.
However, their unbeaten run under Thomas Christiansen was ended by Millwall at the weekend.
Leeds lost 1-0 at the Den, and failed to show their best during the contest, with the Lions picking up a deserved three points.
And Morison has warned his former side that they still have a lot of work to do, if they are to be successful this season.
“Our team was fantastic,” he said.
“People like to write people off and already crown them champions – there’s a helluva long way to go.
“We showed how good we can be and how bad we can make someone else look.”
Morison played the whole game on Saturday, as Millwall beat Leeds and inflicted the Whites’ first league defeat of the campaign.
Leeds will now be looking to bounce back swiftly, with their next match coming against Burnley in the League Cup at Turf Moor.
Leeds reached this stage of the cup, by cruising past lower league opponents Port Vale and Newport County in the first two rounds of the competition.