The Championship outfit make the trip North of the border to face opponents who played their first game ahead of the new season on June 26.
Four defeats from their final six matches last season left Millwall having to settle for 11th position in the second-tier standings, an achievement deemed no more than respectable by Gary Rowett and the club's supporters.
More fresh faces are likely to arrive before their season gets underway at Queens Park Rangers on August 7, but Rowett must first get his players up to speed over the coming weeks.
Millwall currently possess one of the lighter pre-season schedules of the 24 Championship clubs, something which may be amended if Rowett feels that more match practice is required.
Nevertheless, there are plenty of reasons for fans to be optimistic at this stage of the summer as the Lions attempt to build on having established themselves as a mid-table side.
As far as Motherwell are concerned, the 2020-21 campaign was a huge disappointment with the club failing to replicate their third-placed finish from the previous year.
With Graham Alexander in charge, things improved during the opening five months of 2021, but the Steelmen could still only achieve eighth position.
Alexander has since made five additions during the summer window, the most notable acquisition being that of goalkeeper Liam Kelly who has rejoined the club after his previous loan spell from QPR.
Motherwell got their pre-season campaign underway back on June 26 when they suffered a 1-0 reverse at the hands of Dumbarton.
However, with the club's Under-23 players beginning training ahead of the seniors, Rowett will also give game time to some of his younger crop.
Having linked up with Motherwell since their first friendly of the summer, Kelly and Kevin van Veen could both feature for the home side.
Alexander included seven trialists in his squad for the Dumbarton game, but Saturday's lineup is expected to be stronger ahead of the start of their League Cup campaign next week.
We say: Motherwell 1-1 Millwall
With an extra two weeks of training and game time under their belt, Motherwell will start this contest as the marginal favourites. Nevertheless, despite Millwall inevitably using some fringe players, Rowett's side may have enough quality to earn a share of the spoils.