The Reds played out draws with Wacker Innsbruck and Stuttgart in two mini-matches on Tuesday evening, while Mainz opened their pre-season with a 2-1 victory over Wurzburger Kickers earlier this month.
Mainz have firmly established themselves as a Bundesliga side over the last 10 years or so and claimed 12th in Germany's top flight last season, picking up 39 points from their 34 matches.
Die Nullfunfer will be looking to push higher up the division next term, and they have signed three new players during this summer's transfer window, bringing in Silvan Widmer from Basel, in addition to securing deals for Anderson Lucoqui and Lee Jae-sung on free transfers.
Mainz opened their preparations for next season with a 2-1 victory over Wurzburger Kickers on July 9 but have not been in action since. The German side will face Liverpool and Gaziantep FK in their next two matches before taking on Genoa ahead of their return to competitive action in the DFB Pokal on August 8.
Bo Svensson's side will open their 2021-22 Bundesliga campaign at home to RB Leipzig on August 15, meanwhile, which is an indication of the importance of their next two fixtures in Austria, and a strong 29-man squad has made the trip for the team's summer training camp.
Liverpool, meanwhile, started their pre-season on Tuesday evening with two 1-1 draws against Wacker Innsbruck and Stuttgart in Salzburg.
The Reds used 22 players over the course of the evening, which saw them take part in two 30-minute encounters, and there was a debut for summer arrival Ibrahima Konate.
Divock Origi was on the scoresheet in the first fixture of the night against Innsbruck, before Sadio Mane ensured that the Merseyside giants would pick up a draw against Stuttgart in the second contest.
Liverpool will take on Mainz and Hertha Berlin in their next two friendlies before starting next month with pre-season clashes against Athletic Bilbao and Osasuna on August 8 and August 9 respectively.
Jurgen Klopp's side will then open their 2021-22 Premier League campaign away to Norwich City on August 14, and it is going to be fascinating to see how the Reds, who should have Virgil van Dijk and Joe Gomez back in the coming days, perform next term.
Timothe Rupil and Ben Bobzien have also been included from the Under-19s and will be looking to make a strong impression ahead of the start of competitive action.
Svensson will make full use of his squad on Friday, with possibly two different sides featuring in each half, and it will be interesting to see whether those involved in Euro 2020 are thrown straight into the starting XI.
As for Liverpool, Van Dijk and Gomez have both made significant progress in their recoveries from serious knee injuries, but Klopp is unlikely to use either player on Friday night.
Trent Alexander-Arnold was back on Tuesday after recovering from the problem that saw him miss Euro 2020, and the England international could be handed another start against Mainz.
Those involved in Euro 2020 and the Copa America are still absent, but it should still be a strong side for the Reds, with Mane, Origi and James Milner in line to feature from the start.
Harvey Elliott will be hoping to make a strong impression this summer after returning from a loan spell at Blackburn Rovers, and the 18-year-old is set to be involved once again.
Mainz 05 possible starting lineup:
Dahmen; St. Juste, Bell, Niakhate; Kohr; Stoger, Barreiro, Boetius, Brosinski; Onisiwo, Szalai
Liverpool possible starting lineup:
Adrian; Alexander-Arnold, Matip, R Williams, Tsimikas; Milner, Keita, Elliott; Mane, Origi, Minamino
We say: Mainz 05 1-1 Liverpool
This is set to be a tough examination for Liverpool due to the strength of the Mainz squad that has travelled to Austria for the contest. The Reds are in the very early stages of their preparations for next season, and we can see the two teams playing out an evenly-contested 1-1 draw on Friday night.