Wildcards should not be given to players returning from doping bans, says world number one Andy Murray.
Russia's Maria Sharapova has been given wildcards for tournaments in Stuttgart, Madrid and Rome after her 15-month suspension ends next month.
"I think you should really have to work your way back," Murray told the Times.
"But most tournaments will do what they think is best for their event. If they think big names will sell more seats, they're going to do that."
Five-time Grand Slam winner Sharapova was banned for two years after testing positive for meldonium in January last year, but that suspension was reduced in October to 15 months following an appeal to the Court of Arbitration for Sport.