Just be stingy with the red packs....here are some tricks to maximize them.

Play friendlies.
Play friendlies at the end of the league day.
If you need a player tomorrow, heal right after the injury occurs, but leave him with 1 day to heal
If your third best MC or 5th best defender get injured, let him stay injured. Use green packs on the better players since you can't rotate players.
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