I'm a noob here, and that injuries are simply senselless.

Several games in a row my players got injuries that can be cured by 25 red cross packs (5 days), one with 10 (2 days), then again with 25 (5 days); and the pinnacle of the genioussness was today: my player gets injured for 6 days, and my opponent doesn't even get a yellow card, let alone red.
But be assured, as soon as I replaced him, my guy gets a second yellow card, and it's a penalty.

In adding salt to the injury (pun intended) - almost every one of my yellow card players are on the same flank.

All that while I have no idea why are some yellow cards transparent in colour and some are not.