The Englishman highlighted a still from footage of the game at Ibrox apparently showing a Rangers supporter making a monkey gesture. This was captured on Sky Sports and has brought shame on the Scottish game.
Sinclair accompanied the picture with the message #notoracism.
After the match Sinclair tweeted congratulating the team on the win before his message.
The former Aston Villa winger said: “What a team performance yet again, the fans were right behind us from start to finish.
“Just a shame to end the game and seeing the ignorance of people no matter what team u support there is just no need for racism!’
Asked about the incident of a man running on to the pitch, Celtic manager Brendan Rodgers said:
“It’s not nice when something like that happens, but I only caught the tail end of it, really.”
Now Police Scotland have announced that they have arrested a man following the Rangers v Celtic game at Ibrox on Saturday.