Sheffield United: Concerns about striker's fitness confirm why Chris Wilder is so keen to bolster his attacking options

Clarke, United's leading goalscorer last term, is thought to have undergone a scan earlier this week after being ruled-out of Saturday's derby against Leeds.

The 33-year-old, who scored the winning goal against Brentford four days earlier, had volunteered to play at Griffin Park despite being troubled by a minor hip problem.

Although that is not thought to be the source of his latest fitness issue, there are suspicions that featuring in the capital has aggravated a previous complaint.

"We're waiting to see how Leon is," Chris Wilder, the United manager, confirmed. "Hopefully what he's got is not too bad and he'll be available again soon.

"How long he'll be out for is impossible to say at this stage because we're waiting on something. Obviously, fingers crossed, it's nothing major and that Leon will be available again as quickly as possible."

If Clarke is ruled-out of this weekend's visit to Reading, it means United will have only three senior strikers at their disposal for the meeting with Paul Clement's side. 

With only five points separating his sixth-placed team from Leeds in second, Wilder has outlined plans to bolster the attacking options at his disposal during next month's transfer window. But with United scheduled to contest another four games before the market re-opens, Wilder will be keen to see Clarke declared available for selection as United attempt to consolidate their grip on a play-off berth.

"Fair play to Leon, he put his hand up to play (at Brentford)," Wilder said. "It might be that he's not done himself any favours by doing that but we're hoping that's not the case."