Ronaldinho was widely expected to retire from professional football at some point in 2018, but no one expected it to be as soon as January.It was just last month the Brazil legend admitted hanging up his boots was a real possibility in the new year."I think I'm saying goodbye to football next year," he said. "I might play some farewell games for the teams I've played for, it's something we'll have to think about sometime soon."Well, not even a month into 2018 and Ronaldinho has decided enough is enough, as confirmed by his brother and agent, Roberto Assis."He's quit football, it's over," Assis told O Globo, per Goal. "Let's now do something nice, as big as it should [be], after the Russia World Cup, maybe in August."We'll do some events now around Brazil, Europe and Asia. Of course, we're also arranging something with the Brazil national team as well."Nike (Ronaldinho's long-time sponsors) will be with us together on this project, there are no details yet."For now we're arranging a programme, a schedule. The fact he's been Barcelona's ambassador for 10 years now will help a lot abroad. He's held in the highest regard there."There are now three arranged events - Mexico will be the next one, on March 1."Ronaldinho retires as one of football's greatest ever players, having played for the likes of Paris Saint-Germain, Barcelona, AC Milan and, of course, the Brazil national team.Adored yet feared by many, the 37-year-old caused havoc for goalkeepers and defenders throughout his career, especially for a certain Iker Casillas.Casillas, who is currently at Porto, faced Ronaldinho on numerous occasions for Real Madrid and was more often than not on the losing side.But being the class act he is, Casillas has nothing but respect from his old nemesis and today posted a lovely tribute to the Brazilian on Twitter.

CASILLAS PAYS TRIBUTE TO RONALDINHO

In a loose translation from Spanish, Casillas wrote:

"I was forced to suffer at your hands but as a football lover, I also enjoyed watching you."

What a legend. Casillas clearly still remembers when Ronaldinho single-handedly dismantled Real in the the 2005 El Clasico at the Bernabeu.

Ronaldinho scored two goals that day and was so good he received a standing ovation from the home fans - something that will probably never be seen again.