Adam Lallana injured his knee in training and will miss up to six weeks of action, Liverpool confirmed on Friday.
The Reds acquired the 26-year-old midfielder from Southampton earlier this month in a deal believed to be worth up to 25 million pounds, but their new player will miss the start of the season.
Liverpool said Lallana "sustained a knock to his lateral collateral ligament during a session at the Reds' Harvard University training base in Boston."
The injury will not require surgery, the club said.
Lallana, who played for England at the World Cup earlier this summer, will undergo further tests both in the U.S. and England.