Central defender Conall Rawlinson sustained ankle ligament damage in the 4-0 over the Robins on Saturday, wing back Danny Holmes aggravated a hamstring and striker Chris Sharp was concussed after being knocked unconscious.
Matty Williams has also been suffering from a back strain, while Chris Marriott is suspended, leading manager Mike Davies to recall the 20-year-old McKenna and delay a decision on a proposed loan move to Llanelli for wingman Craig Williams.
A former member of the TNS Scholarship Programme who had trials with Ipswich and Preston North End, McKenna made 26 (+22) Welsh Premier appearances for the Saints, scoring six goals, before being loaned to Newtown in the summer to gain regular first-team football.
He scored once for the Latham Park outfit in 13 starts.