Adama Diomande Jayne Kamin-Oncea-USA TODAY Sports

LAFC striker Adama Diomande says he was subjected to racial abuse during Wednesday night's U.S. Open Cup match against the Portland Timbers.

Diomande, who joined LAFC in May, reacted angrily during the second half of his team's 3-2 win at home, and wrote on Instagram after the game that someone called him by a racial slur.

"Today was the first time in my professional career that I was called the 'N' word on the field," Diomande wrote. "They will say sorry to me after the game and please let it go, but If I don't say anything racism will just continue to grow.

"No matter which country, color, religion or which language [you're] speaking we all are human being and we should respect each other no matter what! #saynotoracism"

Diomande did not specify if the slur came from a player or from the crowd, though he was involved in an incident with Timbers players late in the game.

Diomande had words with a number of Timbers players in the 90th minute after a hard foul on his teammate Carlos Vela. They had to be separated and Diomande then attempted to state his case to the referee while Timbers players tried to calm him down.

Then a few minutes later, Portland's Julio Cascante was booked for a late tackle into Diomande's back, and the LAFC man squared up with a number of Timbers players again.

ESPN FC on Thursday morning reached out for comment to both teams and U.S. Soccer, which organizes the U.S. Open Cup.

The Timbers, who are also protesting the game's result over the number of LAFC's foreign players, issued a statement saying the club would investigate the incident.

"The club is aware of the accusations posted on Instagram following Wednesday night's U.S. Open Cup game and is in direct communication with LAFC management, league officials and internal staff to gather more information," the Timbers' statement said. "At this time, we are awaiting more details as we actively continue to investigate the matter. The club will provide further information when it becomes available.

"The Timbers and those associated with the club do not tolerate discriminatory, disrespectful or offensive behavior of any kind, under any circumstances, and it does not reflect the values of the club or the community which it represents."

The Timbers told ESPN FC that MLS would lead the investigation, even though the league did not organize the game.

Diomande, a 28-year-old Norway international, has enjoyed a fine start to life in the U.S., scoring nine times in seven MLS games and was named the league's player of the month for June.

He played in Norway and Belarus before joining Hull City in 2015, helping the club get promoted to the Premier League.

ESPN FC's Jeff Carlisle contributed to this report.