The Blues are in Turkey for their first-leg clash against Galatasaray in the Champions League last 16 but the trip has already been soured by the hospitalisation of two fans
The supporters were both involved in incidents at the same bar on Tuesday night, though they are believed to have been separate instances.
Though the fans have been hospitalised, neither injury is thought to be serious.
Chelsea are conducting an investigation into the incidents and collecting evidence alongside the British Consulate, who are also involved in the process, though responsibility lies with the local Turkish police.
There is a significant precedent to this situation with clashes between Leeds United and Galatasaray fans before a Uefa Cup match in 2000 resulting in the death of two fans of the now-Championship club.
Chelsea face Galatasaray at 19.45GMT on Wednesday evening.