Arsenal manager Arsene Wenger believes some clubs in Europe give their players the performance-enhancing drug EPO.
Wenger has been speaking at a debate in Brussels
He says tests on some new players at Arsenal suggested they had used eryhthropoietin - perhaps unknowingly - before they joined the Gunners.
"We have had some players come to us at Arsenal from other clubs abroad and
their red blood cell count has been abnormally high," said Wenger.
The Highbury boss added: "That kind of thing makes you wonder."
EPO increases the oxygen-carrying capability of blood and Wenger said: "There are clubs who dope their players without the players knowing.
"The club might say that they were being injected with vitamins and the player would not necessarily know that it was something different."
Wenger was speaking at a debate in Brussels on the contribution of football to