Amid speculation over his future, a ‘sore back’ sidelined the Brazilian for the Reds’ final pre-season game against Athletic Bilbao.
Coutinho has been undergoing treatment at Melwood but, with just three days to go, he is yet to return to training.
Liverpool are hopeful the 25-year-old can recover in time for Tuesday’s crucial trip to Hoffenheim in the Champions League play-offs.
Nonetheless, Jurgen Klopp will be without a number of key players for the visit to Vicarage Road, with Adam Lallana and Nathaniel Clyne ruled out.
Daniel Sturridge is also doubtful after picking up a thigh injury against Bayern Munich last month.
Captain Jordan Henderson, though, could make his first league appearance since February after returning from illness.
The injuries mean Trent Alexander-Arnold is likely to start at right-back, while James Milner could be part of a midfield reshuffle.