A police investigation into former baseball star Oh Jae-won's alleged drug abuse has been expanded to other players, who are suspected to have illegally obtained prescription medicine for Oh.

Seoul Metropolitan Police Agency Commissioner Cho Ji-ho told reporters on Tuesday that a total of 13 individuals are being investigated on suspicions of getting prescription Stilnox sleeping pills and other drugs to the former Doosan Bears slugger.

The 13 include eight that the Doosan Bears confirmed involvement in its internal probe into the scandal as well as five additional former and incumbent baseball players, mostly in the second-tier minor league. 

Investigators are probing if Oh pressured the individuals to get him illegally-obtained prescription drugs.

Oh is facing trial on charges of methamphetamine and other illegal substances.