Derek McInnes admitted Aberdeen's midweek Europa League exploits against Real Sociedad played a part as they were defeated 3-0 by Dundee United.
The game was three days after the 3-2 loss and McInnes admitted they did not have enough left in the tank.
"I probably should have made more changes to the starting team," he said.
"The exertions of Thursday night really were evident today and I should have used more of the squad to freshen things up."
Ryan Dow pounced on a poor pass back by Ash Taylor to round Jamie Langfield for the opening goal.
Gary Mackay-Steven added a second leaving the Dons will an uphill struggle, and despite having the majority of the second-half possession Chris Erskine added a late third for Jackie McNamara's men.
"We started fine, kept enough possession of the ball, but without having that real intensity or zip to our play that we normally produce when we're at our best," McInnes told BBC Radio Scotland.
"United capitalised on a mistake and from there on in played with a lot of intelligence and countered on us well.
"We huffed and puffed without ever being convincing enough.
"When we're at our best we show that intensity with and without the ball and it was lacking today, but those performances have been few and far between and I don't expect to see too many of them.
"Goals change games. We felt we started quite positively, we went with two up with Peter [Pawlett] tucked in behind, we wanted to get on the front foot and get the first goal.
"There was a lot of tired minds, tired legs, and we have to aim to be better than that."
Barry Robson was replaced by Adam Rooney with the midfielder receiving a knock in the first half then going down the tunnel with a head knock.
McInnes said: "He was in the wars first half and he was still getting patched up at half-time and we just made the decision to freshen it up and go with Adam, let Peter make his runs from slightly deeper, and I thought he was a constant menace to them in the second half.
"We needed a wee bit more, but Barry should be okay ahead of the next game."