#3 AC Milan - 8 goals
Lionel Messi loves scoring against AC Milan in the Champions League. The Argentinian has netted eight times in eight games in the competition against the Rossoneri.
Messi met Milan four times in the 2011-12 season, scoring once in the group stage and twice in the quarter-final second leg. A year later, he scored twice against them in the deciding leg of the Round of 16. Barcelona won 4-0 after trailing 2-0 from the first leg.
Only a year later, the Argentinian netted thrice in two group games against Milan in the 2013-14 Champions League group stage.
#2 Celtic - 8 goals
Lionel Messi has played only six times against Celtic in the Champions League, but has scored eight goals against them.
He scored a brace in his first game against the Scottish giants in the first leg of the Round of 16, which Barcelona won 3-2 away from home. Five years later, Messi scored against Celtic in Glasgow again, albeit in a losing cause (2-1) in a group game.
In 2016-17, the 34-year-old scored a hat-trick in Barcelona's 7-0 win in a group game. It was Celtic's heaviest defeat in Europe.
A few weeks later, he scored a brace in the reverse fixture in Glasgow.
#1 Arsenal - 9 goals
Lionel Messi has scored nine goals against Arsenal in the Champions League. That's the most any player has scored against a single opponent in the competition after Ronaldo's ten against Juventus.
Messi drew a blank in his first meeting with the English team in the 2008-09 quarter-final first leg, which Barcelona drew 2-2 away from home. However, the Argentinian more than made up for that with a sumptuous quadruple in the return leg.
A year later, Messi scored a brace as Barcelona beat Arsenal 3-1 in the Round of 16 second leg to win 4-3 on aggregate.
In 2015-16, Messi scored thrice across both legs against the same opponents at the same stage of the competition. Barcelona won 5-1 on aggregate.