How can my players keep up with the league level?

[nikolgiorgos]

When can I do this, and aprox. how much boosters to train a team (5-star) to 6-8 star?
Also, no reward videos has came up for a few weeks now.

You need about 200 greens for each player so it's impossible without a lot of farm (still it's not enough) or tanking or buying.

I had two players so far in my team's history, who retired at some high quality (5-6*) but I did tanking (so they lost some good seasons of scoring).
But you know, those players are really rare.