The home side head into this game having topped Group C, while Motherwell face their first match in the competition and hope to improve on last season's effort, having previously lost at this stage.
Both Campbell and Maguire were ruled out of the game just hours before kickoff after they were identified as close contacts with the three Scottish Under-21s players who tested positive for coronavirus during the international break.
The draw with St Johnstone does mean that the Steelmen keep up their good record against the Saints, winning five of their last eight league meetings and keeping a clean sheet in four of their previous seven encounters.
Motherwell have also won their last three matches at home against St Johnstone, scoring eight goals and keeping three clean sheets.
The Steelmen lost 2-1 to Hearts at this stage of the competition last season but a victory on Saturday would see Motherwell qualify for the quarter-finals for only the second time in the last seven years.
St Johnstone have put together a good run of form which has seen them go unbeaten in eight of their last nine matches in all competitions – their only loss being a 4-3 defeat on penalties by Dundee United in the Scottish League Cup, after the match finished goalless.
Callum Davidson guided his side to three wins from four games to top Group C, beating Peterhead, Kelty Hearts and Brechin City, scoring 12 goals across those matches.
The Saints come into this fixture with Motherwell having drawn 2-2 away to Hibernian in the Scottish Premiership on Tuesday, their third draw in four league matches.
A victory for St Johnstone this weekend would see them reach the quarter-finals for the seventh time in the last nine years.
Motherwell form (all competitions): LLWWLD
St Johnstone Scottish League Cup form: WWLW
St Johnstone form (all competitions): DWLWDD
Motherwell pair Allan Campbell and Barry Maguire are self-isolating and so are ruled out of first-team action.
David Wotherspoon, who came off the bench to score against Hibernian in midweek, could be recalled to the starting lineup.
Motherwell possible starting lineup:
Chapman; O'Donnell, Mugabi, Lamie, McGinley; O'Hara, Crawford, Polworth; Lang, Watt, Cole
St Johnstone possible starting lineup:
Clark; Rooney, Keer, Gordon; McNamara, McCann, Craig, Booth; Wotherspoon, Melamed; May
We say: Motherwell 1-1 St Johnstone
Last weekend's draw was the first between the two sides in their last 10 meetings. With the home side having a good record against St Johnstone and with the visitors maintaining their good form we could see another draw at Fir Park, with the match being decided on penalties.