According to the team's website, Fabian Delph suffered a serious knee injury in training on Saturday and had to be stretchered off. Link.
This is obviously scary news, as Fabian Delph must be considered a major part of the team's future. Knee injuries are scary in any sport, but when you're talking about a midfielder who counts speeds as one of his biggest assets, the concern must be magnified.
This is something to keep a very close eye on. One of the biggest reasons to be excited about Villa's future are the young players that have yet to make a major impact on the first team, and Delph is a huge part of that. That's not to say anyone should panic, but everyone should certainly hope that this turns out to be less severe than it sounds.