Chelsea said Friday they had been unable to prove that one of their own fans racially abused striker Daniel Sturridge during the club's Champions League game at Genk.
The London club were looking into claims Sturridge was called a "monkey" as he came on as a substitute in last month's 1-1 draw in Belgium following a complaint from another supporter.
The fan accused of racism - sat in the Cristal Arena's exclusive 100-euro-a-seat section - was alleged to have shouted: "They are bringing on the monkeys."
But none of the 16 fans Chelsea interviewed was able to back up the accusation.
"Following the UEFA match in Genk, Belgium, the club received a report from an executive club member that another supporter had used racially-discriminatory language during the match," a Chelsea spokesman said.
"This was said to have been directed at Daniel Sturridge, who came on as a substitute in the second half.
"As with all such reports, the club takes such issues very seriously and has conducted a thorough and detailed investigation.
"This has involved interviewing 16 supporters who, according to the seating plan, were sat in the area of the stadium concerned. A formal statement was also taken from the complainant.
"In spite of the very lengthy enquiries, the evidence did not identify conclusively any individual as being responsible for making the comments. No other witnesses reported having heard the alleged comments or anything similar.
"In the absence of clear evidence, it is not possible to reach any conclusion on which to pursue the complaint further.
"For these reasons, the club is unable to take any further action.
"We should stress that the club welcomes the diligence of all supporters to report any behaviour which is offensive and unacceptable and will always treat any such complaint seriously."
The accused fan was also alleged to have joined in the abuse of QPR defender Anton Ferdinand during the Genk game.
Chelsea are still trying to identify those heard to chant "Anton Ferdinand, you know what you are" in apparent support for Blues captain John Terry, who is waiting to learn whether he faces criminal charges over claims he used a racial slur against Ferdinand in a recent west London derby.
Terry denies the allegations.