Germany men's volleyball coach Vital Heynen has questioned the attitude of his players, despite sealing top spot in Group B at the European Games.

Victory over Belgium at Crystal Hall on Monday morning was enough for Germany to progress through to the knockout stages.

Regardless of the 3-0 triumph in Baku, Belgian-born Heynen believes his side took their foot off the gas late on.

"We have a lead of 19-13 and I put some other guys in," he told reporters. "It's not about mistakes. You go in [to the court] and do this, this and this. It doesn't matter what the score is, you have to do your job on what we agree.

"Some guys went in and didn't do that. You play to the last point and respect your opponent. You can only say you're better after the match. Not like the third set when some guys come in and smile. No. You play serious volleyball until the last ball."

The men's volleyball quarter-finals get underway on Wednesday morning.