Not every player at Euro 2016 will have been blood tested before Friday's start of the tournament, but the ruling body UEFA plans further tests during the event.
UEFA anti-doping director Marc Vouillamoz said Tuesday that 341 blood tests had been carried out so far, with 552 players in the squads of the 24 teams.
In all, UEFA has conducted 1,278 tests since March in its biggest anti-doping operation on which it is spending 1 million euros (1.1 million dollars.
Vouillamoz said UEFA will have target tests during the June 10-July 10 tournament on those who are yet to submit blood samples. They will also keep an eye on the Russian team amid various doping affairs in the country.
"It's very unlikely that some players won't be tested at all," he said.
All Euro 2016 tests will be analysed at the lab in Chatenay-Malabry, with blood test results available within five hours and those of urine samples after a day.
Apart from out-of-competition tests, UEFA will test two players from each team after each of the 51 games. Samples will be stored for four years and can be retested.
If a player tests positive he will face sanctions but not his team. A whole team can only face punishment if three or more players fail doping tests.