The contest will take place at the League One outfit's training facility in Berkshire as both teams warm up for the new EFL campaign.
Match preview
At one point, putting together consistent seasons in the Championship would have been regarded as success for a team like Millwall, but a mixture of missed playoff opportunities and consolidation has left their fans demanding more.
With Neil Harris now back at the helm, there is optimism that he can deliver on a top-six finish in 2024-25, a consequence of 26 points coming from his 13 matches in charge at the end of last season.
The Lions are still coming to terms with the tragic passing of goalkeeper Matija Sarkic last month, and that will undoubtedly play its part during their preparations for the new campaign.
Each of Millwall's opening friendlies against Bromley and Gillingham have ended in goalless draws, the positives being that the fitness of the squad is on the rise.
Millwall have made three signings during the summer transfer window thus far, with goalkeeper Lukas Jensen, defender Japhet Tanganga and forward Macauley Langstaff all moving to The Den.
Meanwhile, Reading are looking to endure a far less stressful campaign than in 2023-24, where they would have been satisfied with a 17th-placed finish.
Incomings have been few and far between, and may have to wait until later in the transfer window, but Ruben Selles could be content with working with what he has got at his disposal for the time being.
Reading opened up their pre-season campaign with an impressive 2-0 victory over Watford in a behind-closed-doors friendly.
Adrian Akande and Jayden Wareham got on the scoresheet during the second half, giving the Royals some momentum ahead of facing further second-tier opposition.
Reading friendly form:
Millwall friendly form:
Team News
Selles gave his Reading players no more than 45 minutes in the Watford match, something which you would expect to change this time around.
The same starting lineup could plausibly be named, although goalscorers Akande and Wareham did come off the substitutes' bench to make their impact.
Harris will hope to include the likes of Tanganga and Langstaff for this contest after they missed out against Gillingham.
Whether they will start remains to be seen, preference potentially going to the likes of Casper De Norre and Tom Bradshaw who made second-half outings last time out.
Reading possible starting lineup:
Pereira; Abrefa, Mbengue, Kanu, Dorsett, Wing, Rushesha, Savage, Ehibhatiomhan, Camara, Azeez
Millwall possible starting lineup:
Jensen; McNamara, Cooper, Nisbet, Bryan; Watmore, De Norre, Esse, Leahy, Honeyman; Bradshaw
We say: Reading 1-2 Millwall
With both managers likely being keen to step up the intensity, this will be more of a competitive fixture than it perhaps would have been earlier in the month. Reading have already shown in recent weeks that they can compete with second-tier sides, yet we are backing Millwall to edge this contest.