(CNN) -- Luis Suarez illustrated why he is one of the world's most controversial soccer players on Sunday as he appeared to bite an opponent before going on to save his club from defeat with a last-gasp goal. The Liverpool star showed his best and worst sides in a controversial 2-2 draw with Chelsea, and he potentially faces another long suspension after his assault on Branislav Ivanovic. Suarez, the English Premier League's top scorer, wrestled with the Chelsea defender and then clearly sank his teeth into the Serbian's arm. The incident was not seen by referee Kevin Friend, who shrugged off Ivanovic's angry protestations. Suarez later apologized on his Twitter account -- he has been "I'm sad for what happened this afternoon, I apologize Ivanovic and all football world for my inexcusable behavior. I'm so sorry about it!!" wrote Suarez. Among his Twitter followers is former boxing champion Mike Tyson, who infamously bit off part of an opponent's ear in 1997. It is not the first time Suarez has bitten an opponent -- he was suspended for seven matches in late 2010 after an incident while playing for Dutch club Ajax, two months before joining Liverpool.