The Premier League say there were four positive results from three clubs after the third round of coronavirus testing.
These tests were found in the third round on May 25 and 26, when 1,008 people were given swabs.
“Players or Club staff who have tested positive will now self-isolate for a period of seven days,” read a statement.
There are now 12 positive coronavirus cases in the Premier League after three rounds of tests.
It follows the six positives from three clubs in 748 tests in Round 1, while there were two positives from two clubs in 996 tests during the second round.
“For the fourth round of testing, the number of tests available to each club will be increased from 50 to 60.”