In real life, managers, do or sometimes do not, shake the hands or hug a player when they leave the field. You can interact with a player joining the game but can't interact with a player being substituted.
Suggested options
Hand Shake (You are important, I'm resting you for the next match) - good morale booster
Hand Shake (Good game, I'm trying different options) - morale booster
Hug (Brilliant work, take the applause) - great moral booster
No Handshake.