According to fan-group City Watch, De Bruyne picked up the injury during a training session on Wednesday, and could now be facing several months on the sidelines.
De Bruyne previously suffered a knee problem in January 2016 and missed over two months of action for the Citizens.
There has been no word from City on the speculation, although it is thought that the Belgium international will miss at least the remainder of 2018 if ligament damage is confirmed.
The 27-year-old appeared as a substitute in City's 2-0 win over Arsenal in the Premier League on Sunday afternoon.
Last term, the attacker managed 12 goals and 21 assists in 52 appearances in all competitions for Pep Guardiola's side.