No.If a coach/physio needs to come onto the pitch to treat an injury, the player should leave the pitch for 30 seconds before being waved back on.
Is this law applicable to grassroots (open/youth) football?
Around 20-25 seconds from the point we're ready to restart to be semi-precise.Also, in addition to @one 's post, not leaving if the foul results in a caution is providing the treatment is brief. If it's prolonged, then they still need to leave.