Also a flare was hurled in the direction of the visiting players as Mansfield ended Northampton's play-off dream with a 3-1 aggregate victory that booked them a Wembley final.
No one was hurt and security quickly captured the culprits but, 24 hours after Sheffield United striker Billy Sharp was injured by a Forest fan who ran onto the field, Clough was naturally worried and said he felt the current wave of disorder stemmed from the trouble at the Euros final at Wembley last summer.
“This is very concerning and it is very important that security is stepped up now at football matches,” he said.
“This has got to be dealt with and sorted out now. It is becoming a problem.
“Arrests and disorder are up at matches since January. Supporters are not allowed on to the pitch at any time.
“Only the 22 players and the officials should be on the pitch. So stay off it.
“Luckily none of my players have been injured, they are all fine. But this sort of incident has got to be nipped in the bud now.”