The Brazilian looks set to miss the upcoming friendlies with Brentford (Wednesday), Preston North End (Saturday) and Everton (7 August), and also potentially the start of the Premier League campaign, with the Reds kicking off against Leeds United on 14 August.
After regular left-back Luke Shaw revealed he suffered a rib injury during Euro 2020, it will be hoped the England defender is fighting fit for the Leeds opener following an outstanding tournament with the national team.
Tickets for the Everton game at Old Trafford on 7 August are still available.