Nigel Clough admitted the Blades were off the pace for much of Saturday's narrow defeat to Coventry City at Sixfields.
A Bob Harris own goal with 12 minutes remaining condemned United to a second consecutive loss in Sky Bet League One, much to Clough's obvious disappointment.
The Gaffer remarked: "The first 30 minutes were very good indeed, but as good as that was, the next hour or so was poor to say the least.
"The game was flat, there weren't many chances, we certainly didn't create much, but we should have seen the game out at 0-0.
"It would have been our first point, our first clean sheet, it would have been something to build on.
"But we concede another poor goal, which has gone down as an OG and it ends up costing us the game. It was slightly unfortunate, but that is the way it is going.
"The turning point was probably the save their goalkeeper made midway through the first-half, if that had gone in it could have been a totally different game."
The United manager added: "We aren't a settled side yet. Nobody, apart from Mark Howard, is nailed on for a start, we need several players to rediscover their best form and as quickly as possible."