Manchester City's Spanish midfielder Rodri may miss the rest of the season after the injury in the top match against Arsenal.
According to ESPN and Marca, an examination on Monday in Manchester showed that he injured his anterior cruciate ligament.
According to Marca, Rodri has traveled to Madrid where he will undergo further examination.
If Rodri misses the rest of the season, it would be a hard blow for Manchester City, who are chasing their fifth consecutive Premier League title and second consecutive win in the Champions League.
Rodri was substituted in the 21st minute of the 2-2 match.
The 28-year-old midfielder was named the tournament's best player when Spain won the European Championship in Germany last summer, and he is mentioned as a favorite to win the Ballon d'Or, the prize for the world's best player.