Messi is favourite to make it five after a wonderful 2014-15 season which saw him play a lead role as Barca clinched a treble of La Liga, Copa del Rey and Champions League, scoring 58 goals in all competitions. He has managed nine in 13 appearances in 2015-16 after missing nearly two months of action with a knee injury sustained against Las Palmas in September.
The only blemish on Messi's year was Argentina's failure to land the Copa America in Chile. Messi scored in their opening game against Paraguay but then did not find the back of the net for the remainder of the tournament as Gerardo Martino's side lost the final to the host nation.
Ronaldo outscored Messi last season by netting 61 times but Madrid failed to land a trophy in 2015.
The Portuguese has not had a great start to 2015-16 by his lofty standards - despite the statistics showing a record of 16 goals in 20 games. He grabbed five goals in one game and has often cut a frustrated figure under new Madrid boss Rafael Benitez.
Ronaldo himself has said he expects Barcelona's collective brilliance to prove decisive. He told the Jonathan Ross show on ITV: "To be honest I think Messi is going to win this year because this kind of trophy, it depends on votes.
"You win competitions, you win Champions League, you win the league...
"I did probably the best season of my career which is good and I was the highest scorer in Europe [but] it's all about votes, it's difficult and to be honest I'm not very worried about that because as I said many times, I never [thought I'd] win it three times to be honest."
Neymar is the outsider despite a hugely impressive 12 months.
The Brazil captain has become a key member of the much-vaunted MSN (Messi-Luis Suarez-Neymar) combination which contributed 122 goals in Barca's treble - Neymar grabbing 39.
He also proved his growing influence on the Camp Nou side by taking a leading role when Messi was injured.
Like his fellow South American, however, he enjoyed a less successful year on the international stage, seeing red for his part in a mass brawl which marred the group stage defeat to Colombia and missing the rest of the tournament as a result as Brazil were eliminated at the quarter-final stage.
The women's player of the year award will be contested by Carli Lloyd, Aya Miyama and Celia Sasic.
Lloyd was the face of the 2015 World Cup in Canada for her performances for tournament winners United States, Miyama was Japan's captain as they reached the final while Germany striker Sasic landed the Golden Boot.
The winners will be announced at a gala in Zurich on January 11, 2016.
