What is a protected ranking and who is eligible?
A player may petition the Executive Chairman & President for an Entry Protection when he is physically injured and does not compete in any tennis event for a minimum period of six months. The written petition must be received within six months of his last tournament.
The Entry Protection shall be a position in the ATP Rankings, as determined by the player's average ATP Rankings position during the first three months of his injury. The Entry Protection shall be for entry into the main draw or qualifying competition or for special exempt consideration. The Entry Protection shall not be used for seeding purposes, Lucky Loser consideration or for entry into the Nitto ATP Finals.
The Entry Protection shall be in effect for either the first nine tournaments that the player competes in using the Entry Protection (excluding wild cards and entries as a Direct Acceptance with his current position in the ATP Rankings) or for the period up to nine months beginning with the first tennis event that the player competes in, whichever occurs first.
If a player is physically injured and does not compete in any tennis event for a period of twelve (12) months or longer, the entry protection shall be in effect for the first twelve (12) singles tournaments and the first twelve (12) doubles tournaments that the player competes in using the entry protection (excluding wild cards and entries as a direct acceptance with his current position in the ATP Rankings) or for the period up to twelve (12) months beginning with the first tennis event, including Special Events – Exhibitions, that the player competes in, whichever occurs first.
https://www.atpworldtour.com/en/rankings/rankings-faq
