The Red Devils head in to this weekend's fixture high on confidence and in form.
Liverpool have won just 37.5 percent of their games after such a break, but this improves at home, where they have won two of their four games and not lost one, for a win ratio of 50 percent.
Emre Can has told Sport Bild that Liverpool's defensive errors would be less obvious had they been more clinical at the other end of the pitch and said no one at the club is questioning Jurgen Klopp.
At least this time, it is the opener to the Premier League round of matches starting at 12:30 BST on Saturday, rather than the last game as it was on a Monday night in 2016.
When asked whether Liverpool should have strengthened their defence over the summer, he added: "It's in any case a fact that our defending wasn't good recently, and we conceded too many goals".
David De Gea, Antonio Valencia, Chris Smalling, Eric Bailly, Daley Blind, Ander Herrera, Ashley Young and Marcus Rashford will all hope to feature when the boss names his team for what is always a frenzied occasion.
And Klopp will be looking to turn around a poor record in both early kickoffs and in games directly after the international break since his arrival on Merseyside in 2015.
Koeman's side travel to Brighton & Hove Albion on Sunday hoping to avoid only a second loss in 20 against newly-promoted teams in the Premier League.
The midfielder was replaced by Firmino in the closing stages of Wednesday's 3-0 win over Chile, which was enough for Brazil to finish 10 points clear at the top of the South American standings. Some managers might be tempted to go to Anfield and look to dominate.
"But that's football and anything can happen".
Saturday's clash with United comes just under a year after taking on Mourinho's side at Anfield last season, again directly after the October interval. Will Mourinho still see it that way when they return to Anfield on Saturday?