Player Tiers are a way of increasing players’ key attributes and their OVR. Every Tier enhancement means a permanent increase in white attributes that remains active until the player retires. 
Any player is eligible for a Tier increase. There are 6 Tiers, each sequentially increasing the player's key attributes once it's reached. 
Tier  | Permanent Key Attribute increase  |  
Rare  | +10  |  
Elite  | +30  |  
Stellar  | +50  |  
Master  | +80  |  
Epic  | +120  |  
Legendary  | +160  |  
To activate the Stellar Tier, the Elite Tier must be applied to the specific player. In order to obtain the first Rare Tier, a Manager must collect enough complementary (Rare) Tier Points across the game and apply them to the player. Also, Gems can be used as a currency replacement if the Tier requirements exceed the Manager’s Tier Points stash. 
Reminder: Player’s OVR consists of stars (base quality) and Tier increase (permanent key attribute increase). Every promotion in the new season means moving up to a more competitive League, and so the base quality will decrease by 20. This all means that, even with a star loss, Tier’s key attribute increase will stay last until the player’s retirement.