The Uefa make up a club coefficient updated every year depending on the season results in terms of Trophies, goals, assists, participation in European competitions(Champions League and Europa League).
The actual top five of the ranking is made up of three Spanish teams, one German team and one Italian team. This is due to the success of the Spanish clubs, reaching the finals six times in the last ten years. both Real Madrid and Sevilla FC have won the Champions League and Europa League respectively for three consecutive years.
Click on the following link to see the ranking made up by the UEFA.
https://es.uefa.com/memberassociations/uefarankings/club/index.html#/yr/2019
SOCCER STATS 