These two have dominated the Champions League scoring chart year after year, dating back more than a decade. The last player to win the award not named Lionel or Cristiano was AC Milan's Kaka, back in 2006-07.
Since then, Ronaldo has won the Golden Boot six times, Messi five, while the two co-won the award along with Neymar in 2014-15. So is there value in backing anyone else? Let's go down the list and find out.
|Sergio Aguero||Manchester City||8-1|
|Raheem Sterling||Manchester City||12-1|
|Robert Lewandowski||Bayern Munich||14-1|
|Gabriel Jesus||Manchester City||33-1|
|Joao Felix||Atletico Madrid||40-1|
|Alvaro Morata||Atletico Madrid||40-1|
|Luka Jovic||Real Madrid||40-1|
|Eden Hazard||Real Madrid||40-1|
To win the award, history suggests a player needs to be on a successful team. The last player to win the Golden Boot for a club that did not reach at least the semifinals was Ruud van Nistelrooy for Manchester United in 2004-05. The past 14 winners appeared in the semis, with nine of them reaching the final.
The other helpful element is for a player to be drawn into a group with at least one club they can pad the stats against. Messi scored four of his 12 goals against PSV last season, for example, and six against Ajax and APOEL in 2014-15. Ronaldo scored four against APOEL two years ago, and 11 of his 16 against Malmo and Shakhtar in 2015-16.
In order to back a player, you have to be confident in their ability to go far in the knockout stages and in their chances of racking up goals early in the competition. Messi and Ronaldo fit the bill yet again, which their odds reflect, but there are a few others who could push to dethrone UEFA's scoring kings.
Few clubs score goals at the same rate as Manchester City. This season's Champions League favorites have been drawn into a group with minnows Dinamo Zagreb, attack-driven Atalanta, and a Shakhtar side they scored nine times against in last season's group stage.
Sergio Aguero has the shortest odds of any City player to win the Golden Boot, but the 31-year-old striker might not see as many minutes in the group stage should Pep Guardiola decide to preserve him for their domestic duties. Gabriel Jesus could split time with Aguero early on, which would leave Sterling as the attacker with the greatest opportunity.
Sterling started all 10 of City's Champions League matches last season and discovered his scoring touch as the competition wore on, with four goals in his last four matches. He's started this season on a tear after six goals in his first five games, suggesting this could be the year he establishes himself as a consistent scorer.
Icardi isn't going to win any most-liked awards anytime soon, but the striker's innate ability to put the ball in the back of the net is undeniable. A change of scenery - and system - could be exactly what the striker needs to rediscover his form following a falling out at Inter last season.
He scored four goals in six group matches for an Inter side that provided him little service last campaign. Teams would mark him closely, often leaving him frustrated and without much space to operate. Just imagine what he can do this season playing alongside the likes of Kylian Mbappe, Edinson Cavani, and Neymar, for a club that scores goals in bunches.
The free-scoring Serbian is still adjusting to his new surroundings, but he's in an excellent spot to succeed in Madrid. Jovic scored 10 goals in 14 Europa League appearances for Eintracht Frankfurt last season, including two against Chelsea in the semifinals, so he's no stranger to delivering on the big stage.
It helps that Real Madrid's prize signing Eden Hazard will be teeing him up all season. Hazard's 15 assists were tops in the Premier League last campaign for a Chelsea side who had Olivier Giroud leading the line on most nights. Jovic should have plenty of opportunities against a PSG side adverse to defending, as well as Club Brugge, and Galatasaray.
Alex is a sports betting writer for theScore. A journalism graduate from Guelph-Humber University, he has worked in sports media for over a decade. He will bet on anything from the Super Bowl to amateur soccer, is too impatient for futures, and will never trust a kicker. Find him on Twitter @alexjmoretto.