FOr a future update, I think injuries during matches could be improved and split into maybe 3 categories:
1) Serious injuries - they would work like the current injuries do - ie you have to retire from the match immediately. These injuries should be a minimum of 1 week in length
2) Playable - but potentially bad - these injuries give you a choice of whether to play on or not. If you stop play, they are likely to be short injuries - say a maximum of 1-2 weeks out. If you decide to continue play, you have your skills reduced for the rest of the match by 10-20%, and also a chance of that injury turning serious after the match (min 2 weeks out). There is also a chance that you suffer no ill effects after the match and so can continue for the event - this would be similar to the Nadal inury at Wimbledon, where it could have been really bad - but turned out ok.
3) Minor - these injuries (like blisters) don't really require you to retire - but it should be an option. If you choose to continue play, you lose maybe 1-5% skills for that match, if you choose to retire, then they are like the current 1 day injuries.
Yes - this system would mean stopping the match in the middle to ask the user if he wanted to retire - and giving him an idea as to the severity of the injury - but that gives the player a better experience. In the above poster's example, you would simply continue play with the blisters giving you a very small handicap, while in the Nadal situation, it would give you a bigger handicap and potential long term damage - but at least you get the CHOICE whether to risk that.