World ranking leaders Belgium on Tuesday called off a training session for next week's friendly against Portugal in the wake of terror attacks at the airport and a metro station in Brussels in which dozens have reportedly died.
"Our thoughts are with the victims. Football is irrelevant today. Training cancelled," the Belgian football federation KBVB said on Twitter.
Belgium are due to play Portugal on March 29 in Brussels'Stade Roi Baudoui stadium where Tuesday's training session was also originally planned.
The Portuguese federation FPF said in a statement on its website it was in contact with the KBVB. Portuguese sports paper A Bola said it was doubtful the game would take place.
Belgium has raised its terror alert level to 4, which indicates a "serious and imminent" threat.
Last November, a Belgian friendly with Spain was called off in the wake of the terror attacks in Paris.
"My thoughts are with the victims and their family!" Belgium goalkeeper Thibaut Courtois tweeted, and midfielder Kevin de Bruyne said on the same social network over a heart in the national colours: "Unbelievable! 'PrayforBelgium".
Lowly English Premier League club Norwich said that their Congo striker Dieumerci Mbokani was visiting familiy members and at Brussels airport at the time of the attacks.
Norwich said Mbokami "was unharmed but shaken by the tragic events ... The Club is in constant dialogue with Dieumerci, who has now returned home to be with his family."
The Brussels incidents are also discussed among the German team which was playing France on November 13 at the Stade de France which was one of the targets of the Paris attacks.
Germany's November 17 match against the Netherlands was cancelled after a terror threat and they now play England in Berlin on Saturday and Italy on March 29 in Munich.
"It will definitely be an issue that will on the players' minds in the wake of the Paris events," Germany general manager Oliver Bierhoff said.
Defender Shkodran Mustafi said: "If you have been personally involved you know how the people there (in Brussels) feel."