Nato leaders have informally agreed not to mention the football World Cup to Donald Trump in case they irritate the US president at a crucial time for the military alliance.

Officials said European leaders had discussed in the sidelines of the summit in Ankara how to keep Trump on side amid concerns he could further destabilise Nato with threats over defence spending.

They are already working together to reassure the US president they are pulling their weight financially by building “a stronger and more European Nato” with each member on track to spend 5% of GDP on defence by 2035.

In the first open acknowledgment of the strategy, the Belgian prime minister, Bart De Wever, told reporters in Ankara that he would not be discussing his country’s 4-1 win over the US earlier this week.

The summit follows a row caused by Trump asking the Fifa president, Gianni Infantino, to review the red card shown to US striker Folarin Balogun, meaning that he could then play in the match against Belgium.

Ahead of their meeting at the summit, De Wever joked to reporters that the US president “has the reputation of sometimes reacting a bit irritably to things that he doesn’t like, and I think this defeat will hit hard”.

The Belgian leader said his country’s footballing triumph against the US had dominated his early discussions in Ankara. “Everyone’s talking about one thing, and that is congratulations for the well deserved victory of the Red Devils,” he said, the nickname for the national side.

“Of course, the losing party is also present. That also happens to be the biggest partner in Nato.”

Asked whether he was worried that Trump could be annoyed that the US had dropped out of the tournament, he told the Flemish broadcaster VRT: “I’m not going to start [talking] about it myself. But if he were to say something about it, then I’ll see what that is and how I can react to it.”

Trump has yet to comment about the US team’s defeat, but was mocked during the match by several Belgian players mimicking his signature dance move after their fourth goal.

In the run-up to England’s quarter-finals match against Norway on Saturday, Keir Starmer teased his Norwegian counterpart that England “only win the World Cup under Labour governments”.

The prime minister exchanged banter with Jonas Gahr Store after a meeting in Ankara during which they both wore their own national team shirts.