The Portuguese has won the prize on four occasions, but is way behind the Argentine this term as the Barcelona forward closes in on a fourth award
Ronaldo has claimed that honour more than any other player, winning it four times - in 2007-08 (with Manchester United), in 2010-11, 2013-14 (tied with Liverpool's Luis Suarez) and 2014-15.
However, Messi has taken home the award on three occasions - in 2009-10, 2011-12 and 2012-13 - and the Barca forward looks set to win it again this time to draw level with the Portuguese attacker.
Messi has hit 33 goals in La Liga so far in 2016-17, eight more than team-mate Suarez (on 25), while he is also 13 clear of Cristiano (20) in the current campaign in the Primera Division.
With Ronaldo regularly rested in the league to keep him fresh for European action, the Portuguese is unlikely to be able to close that gap now, although it has paid dividends because his eight goals in the last three Champions League clashes (two versus Bayern Munich and one against Atletico) have left Madrid on the verge of another final in that competition.
Cristiano could also draw level with Messi in the Ballon d'or later this year as he aims to win the individual award for a fifth time.