Belgium coach Roberto Martinez acknowledged his side produced an unacceptable display against San Marino despite a 4-0 victory.
Martinez’s side are top of Euro 2020 Group I after they made it five victories from as many qualification matches.
However, Belgium’s performance against a spirited San Marino side, especially in a first half, was sluggish.
San Marino are bottom of the FIFA world rankings and have not earned a qualification point since November 2014 while Belgium are top of the rankings and reached the semi-finals of the 2018 World Cup.
The scoreline was goalless for the first 43 minutes until Belgium opened the scoring for the penalty spot through Michy Batshuayi.
Second-half goals from Dries Mertens, Nacer Chadli and a second from Batshuayi sealed the result but Martinez was far from satisfied.
"I'm not happy with the way we played," said Martinez, whose acknowledged his side must improve when they play Scotland at Hampden Park on Monday.
"It wasn't good enough or up to our standard. It's true in the first half we didn't look like a team with direction".