Fans of Turkish club Fenerbahce have apparently hacked into Spartak Moscow's website, two days after the sides met in a fiery Champions League play-off encounter in Moscow.
Spartak won the first leg 2-1, the winning goal coming from winger Dmitry Kombarov.
But the match at Moscow's Luzhniki Stadium also saw some tense moments in the stands, as a section of Spartak fans held up anti-Muslim banners and allegedly burned a portrait of Kemal Ataturk, the founder of the modern Turkish state.
In response, Turkish hackers apparently attacked Spartak's official site on Thursday morning, placing a picture of Ataturk on the homepage.
Alongside the picture was a message, written in Turkish, which read: "Apologise immediately to the Turkish people. FIFA will ignore this, but we will not allow this crime to go unpunished."
The site was then taken offline, and remained inaccessible on Thursday lunchtime.
Tensions have mounted around the second leg of the match in Istanbul, with fans of Spartak fearing reprisals from their Fenerbahce counterparts.
"The Turkish side have guaranteed our security in the away leg," Spartak's official fan-club director Oleg Semenov told Russian website Championat. "We will discuss whether to bring with us members of the Russian police force.
"UEFA have been informed about what is happening."
The second leg will take place at Fenerbahce's Sukru Saracoglu Stadium on Wednesday 29th August.