Leeds United striker Billy Paynter is facing more time on the sidelines after suffering a setback in his fight against injury.
Paynter looked to be closing in on a belated first-team debut following his appearance in a behind-closed-doors friendly last week but he was ruled out of Tuesday's reserve game at Middlesbrough and is back in the hands of specialists.
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The 26-year-old's short time at Elland Road has been dominated by the damage he sustained to a shin during the early stages of United's pre-season campaign.
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Paynter has not played in a first-team game since Leeds' clash with Slovakian club MFK Kosice on July 16 and he is still waiting to make his competitive debut, three months after moving to Elland Road on a free transfer from Swindon Town.
Grayson said: "He's had a slight reaction to his injury and he's gone away to get some tests done.
"We'll have a bit more news after the weekend but it's disappointing because he was building up his fitness and got a game in last week. We don't know the severity but we'll have to see where we are now."
Paynter's latest blow has ruled him out of tomorrow's Championship game against Sheffield United, and injury is also set to prevent defenders Paul Connolly and Federico Bessone from playing at Elland Road.
Kasper Schmeichel, Ben Parker and Patrick Kisnorbo remain on the absentee list but Leeds have confirmed that a complication with the paperwork held by recent signing Ramon Nunez has been resolved, allowing the Honduran midfielder to be considered for selection.