Swindon Town manager Paolo di Canio has clashed with one of his players.
After his side were beaten 3-1 at home in their second-round clash at the County Ground, the hot-headed Italian could be seen remonstrating with forward Clarke as the team left the pitch.
The former West Ham striker appeared to manhandle Clarke towards the tunnel and the pair seemed to be pushing and shoving before being separated.
Swindon chairman Jeremy Wray, who has promised to conduct a full investigation, said: "Clearly there was an incident and it would be wrong to apportion blame until we have all the facts.
"Leon and the fitness coach were having words after the game and there was a disagreement between them. As Leon came off the pitch Paolo was conscious these things should be done behind closed doors.
"There was a misunderstanding there that carried on into the tunnel.
"It got to a situation where the whole thing blew up very fast. There was frustration on both sides.
"The whole issue was trivial but nobody responded in the right way.
"The manager was quite right to try to defuse the situation.
"Paolo was frustrated the whole thing was played out in public. He feels one of the players has let him down."