Coke is actually as good as most so-called sports drinks when diluted down - which Monfils may have done. A drink doesn't need to have a sportsy name or a picture of a sweating athlete on it to be legit for use during sports.
During the 80s many tennis players drank watered down coke as their in-game drink. I grew up doing it and, when short on a better alternative, still do sometimes.
Original Pro Staff 85, leaded to 370g, hybrid poly/syn gut set-up, 48-52-ish lbs.