This may be more important then you think.
If we had a dollar for every time we were asked what to do to help a groin pull we would not even need this web store. We could pay all the bills on this one question.
The key is to not get the groin injury in the first place.
For most lifters everything they do for the lower body involves pushing the knees out to the side (squats, pulls, good mornings). It would be bad form to drive your knees in. Plus you would blow your knee off and this would not be good.
This may lead to muscles imbalances between the abductors and adductors. These muscles do not have to be in perfect balance but it does not hurt to work the weak link.
First wait until you are alone or nobody is looking. Then hook up this strap to a low cable unit. You can work all four directions but should be more concerned with pulling the leg in and across the body.
If you want to be cool...
Hook this up on your sled strap and do the same thing while dragging a sled. This will save face as this is much, much tougher than doing it on the functional trainer in the gym. Great for hip addduction/abduction and sled dragging. Also great for different kinds of pulls (lat work) and triceps work for those who have an injured hand. Price is for ONE strap.
Price is for one strap.