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Roma midfielder Radja Nainggolan has announced his retirement from international football after he was left out of Roberto Martinez's provisional Belgium squad for the 2018 World Cup.

Per Sport Witness, he revealed the decision on Instagram:

His exclusion from the squad was perhaps not too surprising, as Nainggolan played just six minutes of their qualifying campaign to reach the tournament in Russia.

The midfielder was reportedly dropped by the Spaniard initially because of his smoking habit, though Martinez said it was a tactical decision:

Football journalist John Solano was critical of the snub:

Martinez recently signed a two-year contract extension with the Red Devils, so Nainggolan's chances of playing a significant role after the World Cup appeared to be slim. 

Given he's now 30, it's understandable he has taken the decision to call time on his Belgium career.

His absence is a blow to the national side, though, such is his quality.

As Squawka Football demonstrated, Nainggolan is a potent blend of combativeness and creativity in the centre of the park:

Belgium are hardly short on midfield talent, and they were able to qualify for the tournament largely without Nainggolan, but few can make things happen like he can or contribute so much both offensively and defensively.

To not even have him as an option in the squad is a strange decision if it was made for tactical reasons.