Sheffield United manager Kevin Blackwell has revealed all three of his current trialists have plenty to do if they want to win a permanent deal at the club.
Blackwell is in the hunt for new defenders and handed trials to Manchester City's Shaleum Logan, Birmingham's Gregory Vignal and Kerrea Gilbert of Arsenal earlier in the week.
But the Blades boss said: "I doubt any of them will sign but we've got to try and unearth a little diamond somewhere and we keep looking."
He added: "We know who we want and Trevor Birch has worked exceptionally hard to get the players in and we continue to do that.
"When you look at the players we've brought I want people to regard them as good signings that will improve the squad for some time to come.
"The three we have this week have got work to do yet and the trial has to end sooner or later so Friday is their D-day."
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