On-loan striker Vokes has been refused permission by Wolverhampton Wanderers to play in United's FA Cup first-round tie against Oldham Athletic and Kandol – his most likely replacement – is also retiring to the sidelines this weekend after incurring a three-match ban for violent conduct.

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The former Barnet player received the punishment following an incident at the end of last weekend's 4-0 victory over Yeovil Town and the suspension has denied him the chance to reunite his partnership with Jermaine Beckford.

Kandol had put himself in contention for selection with three goals in five appearances, but his absence is expected to mean that either Grella or Showunmi starts alongside Beckford, the club's leading scorer.

Both Grella and Showunmi have been peripheral since Vokes was signed on loan last month, but the first-round tie at Boundary Park presents an opportunity for one of them to reclaim a place in Grayson's plans.

United's manager is unable to call on Luciano Becchio with the Argentinian striker recovering from an ankle injury, while on-loan winger Max Gradel is also prevented from playing at Boundary Park with Championship side Leicester City unwilling to see him cup tied.

Grayson is expected to be without goalkeeper Shane Higgs and midfielder Andy Robinson, both of whom have been suffering from muscle strains for the past month, but Rui Marques resumed full training towards the end of last week and is not far away from overcoming his Achilles problem.

Ben Parker is a long-term absentee after hip surgery.