If you have to retire from a tournament it is important to indicate this in ManageMyMatch. It allows the system to abort any matches and to inform your opponents of the situation and allows the tournament to continue in your absence.
Find the tournament from which you have to withdraw in the In play section of My events. Click the red Leave button. You'll also get an opportunity to do this from the home page.
If you decide you can rejoin then you'll find that just as easy as the Leave button will have been replaced by a Rejoin button.