Major League Soccer Monday announced the introduction of concussion substitution trials for the 2021 season with two additional changes for suspected head injury victims allowed outside of the regular five that will continue into the new campaign after being introduced last year. U.S. Soccer and all professional leagues in the United States will implement the same rule.

The International Football Association Board (IFAB) approved trials for concussion substitutions back in December of 2020 and the system was consequently introduced in the Premier League and Women's Super League (WSL) until the end of the 2020-21 campaign back in February.

With these trials in place, MLS will ensure the safety of players without putting teams at a competitive disadvantage by allowing permanent withdrawals from the field instead of temporarily playing on with 10 men while a decision is made.