Joey Barton reportedly headbutted and punched rival manager Daniel Stendel after Saturday's match at Oakwell.
Police are investigating an incident in the tunnel involving the controversial Fleetwood boss.
Barnsley striker Cauley Woodrow tweeted that Barton confronted Tykes manager Stendel following the game, which ended in a 4-2 victory for the home team.
The tweet has since been deleted.
And according to The Sun, Barton headbutted and punched Stendel before grabbing him by the throat. Stendel reportely lost two teeth in the attack.
A South Yorkshire Police spokesman said: "We are aware of something that has taken place in the tunnel after the game and we are investigating."
Joey Barton investigated by police over alleged assault of Barnsley manager
Woodrow, who scored in his side's victory, claimed Stendel was left with "blood pouring from his face".
Neither club fulfilled their post-match media duties after the match, which saw Fleetwood have Harry Souttar sent off after 65 minutes with Barnsley leading 2-1.
Barnsley said in a statement: "The club can confirm there was an alleged incident in the tunnel area that took place following the conclusion of today's match, which South Yorkshire police are currently investigating.
"The club is assisting the police with its enquiries and, as a result, we are not in a position to make any further comment at this time."
Footage tweeted by Sky Sports News showed Barton leaving the ground, but the car he was travelling in was stopped from leaving the stadium's car park.
Chief executive Shaun Harvey has promised the EFL will help investigate an alleged incident involving Fleetwood manager Joey Barton at Barnsley.
Barton is said to have confronted Reds boss Daniel Stendel in the tunnel following Saturday's game, which ended in a 4-2 victory for the home side at Oakwell, and South Yorkshire Police are investigating.
Harvey told BBC Radio 5 Live's Sportsweek programme: "As an off-the-field matter the tunnel is still in the domain of the referee but we will work closely with everybody to ensure it's not a case of who deals with the matter but actually the matter is dealt with properly.
"The police investigation is ongoing so we need to leave the details for them to deal with."
