Sheffield United boss Chris Wilder hopes to sign a defender after confirming that Jack O'Connell is likely to be out for the season with a knee injury.
The 26-year-old was absent on Sunday afternoon as the Blades slipped to a 1-0 home defeat against Yorkshire rivals Leeds at Bramall Lane.
The club announced on their Twitter account before kick-off that O'Connell needed an operation and after the match Wilder shed some more light on the matter.
"Jack O'Connell is possibly out for the season. He will have an operation on Wednesday and we are looking at six months minimum," said the Blades boss.
"He was having discomfort and some issues with his knee and from a long-term point of view it was not good for him to carry on how it was.
"He's an important part so we need to cover that situation. For him to potentially be out for the rest of the season is a blow.
"I've spoken to the owners, as obviously we've known this for two or three days and we need to bring someone in in that position. We are light and can't solely rely on Jack Robinson playing that position all the way through.
"I've highlighted a couple of players and hopefully the board will agree with my assessment that we need to strengthen."
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On the pitch, Wilder saw his side's losing start to the new season continue after Patrick Bamford's late header.
The 27-year-old nodded home Jack Harrison's cross after 88 minutes, finding the net for the third straight Premier League game since Leeds' promotion back to the top flight.
There was little Blades goalkeeper Aaron Ramsdale could have done, having otherwise produced a fine individual display.
At the other end, Illan Meslier also shone between the posts for the visitors in a match that looked destined to finish goalless until Bamford struck.
His goal sealed back-to-back Premier League wins for Marcelo Bielsa's side while the Blades have lost all three of their Premier League fixtures this season and have yet to score a goal.
Wilder said: "I thought it was really tight game - a Yorkshire derby it was always going to be that way. They are an exceptional side, some really good players and a great coach.
"We had the better chances, especially in the first half, and if you don't take your chances in a tight game then you get punished.
"I don't agree with Marcelo's opinion that they deserved to win. We had the better chances and we had to score.
"Aaron didn't get the man of the match like their goalkeeper did, so I don't think he had that much to do. Maybe I'm looking at it through rose-tinted glasses.
"The three games we've played there's not been a lot in them. We just need to be more clinical - fine margins. I personally feel we deserved to win the game based on the chances we created, we created the clearest chances, but we didn't take them and we have paid the price."
Leeds boss Bielsa believed his side were worthy winners after growing into the match and improving in the second half.
"We could have gone in ahead or gone in at half-time behind," said Bielsa. "But in the second half we were better and dominated a bit more, more opportunities, and I think the result in the end was a just one.
"I am pleased with the defensive performance of the team. In the first two games we didn't defend as badly as to concede seven goals and not to concede in this game is a step forward. Illan Meslier made some very important saves.
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"I am not a specialist in evaluating goalkeepers but he is a player with huge character and personality and he has qualities both making saves and with the ball at his feet.
"In the second half we had an extra energy. It is always hard to tell whether this is because the opponent is worn out a little bit or if we are putting in extra effort.
"I think we played at the same rate but found it easier to build our attacks, causing imbalances with [Stuart] Dallas, [Luke] Ayling and [Rodrigo] Moreno. We deserved it."