The two footballing icons spent six years playing together, first at Barcelona for four years, before Messi joined Neymar at Paris Saint-Germain in 2021.
Both stars left the Ligue 1 giants this summer, with Messi linking up with MLS side Inter Miami, while Neymar joined Saudi outfit Al Hilal.
But the Brazilian's £86million move to the Middle East hasn't gone to plan.
After missing the opening four Saudi Pro League matches with muscular problems, the 31-year-old is now having to have surgery.
Neymar ruptured his anterior cruciate ligament and suffered a meniscus tear injury while playing against Uruguay on Tuesday in a World Cup qualifying match.
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Al Hilal have since confirmed he will have to have surgery.
Given ACL injuries normally take six to nine months to recover, Neymar's 2023/24 season is seemingly over.
Now, Messi has reached out to his friend to send him support following the news.
"Much strength Neymar!" Messi wrote in Spanish on his Instagram story, along with a photo of the pair embracing from their time at Barcelona.
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Messi and Neymar won eight trophies together, including a Champions League in 2015 with Barcelona.
They formed one of the best front threes in football history alongside Luis Suarez at Barca, before making up PSG's attack alongside 2018 World Cup winner Kylian Mbappe.
Prior to his injury, Neymar had chipped in with one goal and three assists in five games in all competitions for Al Hilal.