David Flitcroft said a poor start to the game from his Mansfield Town players contributed to their defeat at Port Vale.
The Stags missed the chance to go ahead in the first half when Nicky Ajose saw his penalty well-saved by opposing stopper Scott Brown.
Ricky Miller, who had a loan spell with the Stags in early 2018, scored a quick-fire brace to put Port Vale in control at Vale Park.
Ajose halved the home side’s advantage but Mansfield were unable to get a second to salvage a point in what was a third straight away loss for Flitcroft’s Stags.
“I think the start was poor,” said boss Flitcroft. “We didn’t start well. We were loose and untidy in our work.
“That gave them a lift first half and we kept giving them lift after lift.
“Whether that’s a misplaced pass or an untimed run or a bad angle, we gave them lift after lift and encouragement after encouragement.
“We weren’t at our best. I look at the second goal and that’s as poor a goal as you’re going to see.
“It ricocheted and we didn’t clear our lines.
“We’ve prided ourselves on clearing our lines all season, concentrating on our work.
“There was a change to the back three, to the back four, and it looked like that today.
“It looked wrong.
“Sweeney’s had to come off but again I’m disappointed with how that’s happened.
“He’s taken a whack to the head, a big smash to the head, and he didn’t let us know how he was feeling.
“I love Sweenes but he’s got to make those decisions. He’s come out at half time and still feeling groggy.
“He’s fallen down on the pitch and they’ve score in that moment.
“That’s not professional for me, that, and I’m going to look into that and how it’s happened.
“It’s small detail but it’s massive.
“There’s a consequence to everything.
“We’ve not been at our best today and we’ve given Port Vale too many leg-ups today.”