I wondered that too. Keep an eye on it and see if gets little purple/blue flowers.
||Ground ivy looks a good possibility.|
||I'm going to say no to ground ivy, your photo doesn't show alternately opposite leaves (unless the pair on the top had one leaf ripped off). Your photo looks more like a single leaf with three leaflets than a stem with three entire leaves (unless I'm way off here?)|
||What sort of environment is it growing in, soil type, vegetation type and that?|
I think I could be on to a winner.