Manchester City winger Oscar Bobb is set to miss the start of the season after breaking a bone in his leg, a source has confirmed to ESPN.

Bobb suffered the injury in training on Wednesday after trying to turn. According to a source, no other player was involved in the incident.

The 21-year-old will undergo further assessment before a decision is made on the next steps for his rehabilitation. It is not yet known how long he will be out of action but he will miss City’s opening Premier League games.

Pep Guardiola’s side start their title defence against Chelsea at Stamford Bridge on Sunday.

Bobb’s injury is a blow for City after the Norwegian impressed during the preseason tour of the U.S. and the Community Shield victory over Manchester United. He set up the late equaliser for Bernardo Silva at Wembley before City won on penalties.

Bobb’s absence will further reduce Guardiola’s attacking options. Julián Álvarez has left the Etihad Stadium to join Atletico Madrid in a deal which could rise to £81 million ($103.9 million) and Jack Grealish is a doubt to face Chelsea after missing the Community Shield with an injury.

Bobb had been tipped to play a more important role for City this season after scoring two goals in 26 appearances last term.