Japan's professional football league is investigating a reportedly racist banner, reading “Japanese only”, displayed at a weekend's Japanese League (J-League) match between Urawa Red Diamonds and Sagan Tosu (08 March).

The large banner, written in English, was hoisted near a gate to the stands of the Saitama Stadium 2002, in greater Tokyo, where the home club Urawa Red Diamonds were taking on rivals Sagan Tosu.

At the time, social media speculated that the sign could have been targeting South Korean-born striker Tadanari Lee.

Lee, who also holds Japanese citizenship, was released by the English club Southampton for a transfer to Urawa before the J-League season kicked off this month.

Urawa said Sunday it was questioning an unspecified number of people who had displayed the banner, which also featured a Japanese flag, saying their “words and deeds evoked discrimination”.

“Staff from a security guard company in the stands has reported that discriminatory remarks were heard during the match,” said the statement.

Sagan's manager and coach are both South Korean, as are several players.

Urawa defender Tomoaki Makino tweeted after his team's loss on Saturday that “this is not the way to treat players who fight for this team with pride”.

“Players and supporters cannot unite as one and produce results this way,” he wrote.

Urawa, the 2007 Asian champions which draws passionate backing from its large fan base, said the results of its probe would be released to the public.

“Discriminatory remarks and actions cannot be condoned,” it said.

J-League chairman Mitsuru Murai told Japanese media on Sunday that “we will deal with it in a stern manner” if the message was proven “discriminatory.”

The Japan Football Association had no immediate comment.

From Fox Sports