The team sitting at the bottom of the Pro League table come the end of the season will automatically be relegated to the Premier division, whose winner will secure a berth in top division.
Teams ranked tenth and eleventh in the Pro League will take on the second and third-placed teams from the Premier division in a relegation stage to determine the final two teams in the next Pro League season.
Quelle: http://www.hltv.org/news/15194-esl-explains-pro-league-relegation