We have been fortunate in southwestern, Pennsylvania to have had a relatively mild winter to this point. Although I hear there is snow in the forecast for tomorrow. Eeeek!
My son and I have been able to get outside and play a little footie from time to time on the mild days which has helped pass the time during winter. Side note : not the greatest fan of this time of year.
Getting touches of the ball in, even when it's cold and yucky outside, does not have to happen exclusively on grass or outside.
Don't fall into the trap that soccer practice only happens during team practice each week.
All your player needs is some motivation , a flat space (basement, garage, family room), and some time. This is an example of an exercise or group of exercises where a little bit of work goes a long way to them becoming a better player. Some of these are advanced drills but many are the foundation for good, solid, footwork.
The term "technically skilled" in soccer/football is based around the idea that a player has strong fundamentals. I want each of my players to be "technically skilled" among other things (having a soccer IQ, creative, and having passion for the game).
Here are some things your player can be doing now to improve their foot work. Video courtesy (The Soccer Essentials)