Ludogorets Razgrad must play Real Madrid in its Champions League group-stage home debut with a stadium section closed because of fans' racist behaviour.

UEFA says its disciplinary panel imposed sanctions after incidents when Ludogorets eliminated Steaua Bucharest in a playoff last week.

Steaua was also punished for fans' racist behaviour and must play a Europa League match in an empty stadium.

Ludogorets hosts Madrid on October 1 in the National Stadium, Sofia. Its own ground does not meet UEFA standards.

UEFA fined Ludogorets 16,000 Euros ($A24,000) for fans invading the field and the team receiving at least five yellow cards.

UEFA ordered Steaua to play Aalborg on September 18 without fans, for their second racist offense this season.

Steaua was fined 64,500 Euros ($A96,745) for the racism and other offenses.

UEFA operates an escalating scale of sanctions with further racism incidents provoking full stadium closures, leading to possible disqualification from competitions.

"All forms of racist behaviour are considered serious offences against the disciplinary regulations and are punished with the most severe sanctions," UEFA said.