Sunderland injury news: Corry Evans update after first Championship defeat
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The Black Cats impressed through the opening half hour at Bramall Lane but the game turned when Dan Neil was shown a red card for a professional foul on James McAtee, with Anel Ahmedhodžić scoring from a corner shortly after.
It looked an uphill battle for Neil's side when Max Lowe scored early in the second half, but they reduced the deficit through Lynden Gooch in a spirited performance.
"I'm proud of the players and how they went about it," Neil said.
"We've made an error in the game and that can happen, particularly if you go and risk the ball like we did tonight. They capitalised on it, and the job then becomes really, really difficult at that point.
"I thought the way the lads went about it, their effort, their understanding of still trying to carry a threat and to play when we had the opportunity to do so... the effort levels were through the roof.
"Sheffield United are a very good team and for thirty minutes we more than matched them, if anything looked a bit more threatening.
"We were really good, and then after that it's difficult. The one frustration is probably the second goal, you come out at the start of the second half and the next ten, fifteen minutes you need to keep it as tight as you possibly can, and then you can try and go and nick it.
"The response to that was really good.
"I've absolutely no complaints in terms of what the players put up, I thought they were brilliant."
Dan Neil had been forced into a more defensive role due to an injury to Corry Evans, which remains a major concern for the Black Cats.
"It's easy for me to go and try and put a player in that deep-lying role, to stifle and make tackles, but I felt that if we were to come here and win, we needed to control the ball deeper and risk the ball," Neil said.
"Embo and Dan Neil up until the red were excellent, the front two were a handful, we got balls in the box. I was really pleased.
"I thought Dan was brilliant up until the red card. He landed on things, he made tackles, covered the ground well and found good positions to link it and switch it.
"All the bits we asked him to do, he did really well. Unfortunately for him the ball comes in, it's a slippy surface, it just takes off his left foot and the lad lands on it. It happens, it's a learning curve for him. We're frustrated for him, we know how good he is, and up until then he was great.
"Corry is out unfortunately at the moment," Neil added.
"I've not got a timeframe at the moment. With Dan Ballard out, Corry out, it becomes difficult doesn't it?
"But to a man, I was really pleased. We made five substitutions and the people coming on showed real application and effort for the team and the supporters."