Thordarson parted company with the Railwaymen on Friday morning following their disappointing start to the season and with no immediate plans in place to find a replacement, Gradi has stepped in to take over first-team duties.
The 68-year-old will have to make do without captain Billy Jones and fellow defender Patrick Ada.
The duo were sent off late in the home defeat to Bury in midweek and must serve one-match bans. Jones was sent off in the 85th minute for a foul on Shakers skipper Stephen Dawson, while Ada was dismissed in injury-time for a challenge on Michael Jones.
On-loan goalkeeper David Button could be a surprise inclusion in the squad after Tottenham allowed him to return to Gresty Road.
The 20-year-old missed the 5-3 defeat at Accrington because of a back problem, with Alex signing Adam Bogdan on loan from Bolton for the visit of Bury while Button received treatment back at his parent club.
However, Button has trained this week and will challenge Bogdan, Adam Legzdins and Steve Collis for the number one jersey if he suffers no reaction.