He tweeted earlier...
Gael Monfils @Gael_Monfils 36m
Parfois pour avoir un arc en ciel, il faut avoir des gouttes de pluie...
*The English translation is: Sometimes for a rainbow, you need raindrops...*
It has a very sombre, dark feeling and perhaps meaning to it. Maybe one of his parents have died?
That particular tweet doesn't make much sense if it's a death, although his later one would suggest that.
Monfils was reportedly doing his usual clown act on court yesterday, and said afterwards "I was happy, I was having fun", so it sounds like he got the news after the match - yet it would appear that the French Tennis Federation tweeted the news of his withdrawal from Wimbledon earlier in the day. All very strange, although perhaps by playing he was able to put whatever it is at the back of his mind for a while - and, believe it or not, that isn't impossible even after the death of somebody close to you once the initial shock has passed, although it'll catch up with you quickly enough once there's nothing to distract you.