A supporter was arrested after confronting Arsenal manager Arsene Wenger in his dugout during the Gunners' 2-0 defeat at Southampton.
The 25-year-old man approached Wenger, 65, but was led away by stewards and detained by Hampshire Police.
Southampton say the man was an Arsenal fan sat with home supporters but Wenger thought it was a Saints' follower.
The incident comes after Wenger was abused by Arsenal fans when boarding a train after December's loss at Stoke.
At St Mary's, Wenger's assistant Steve Bould angrily gestured to the supporter who was guided straight down the tunnel by a group of stewards quick to react.
"It was a young boy," said Wenger afterwards. "I think it was a Southampton fan. He was not aggressive at all. I don't think he said anything."
A Hampshire Constabulary statement read: "The man, arrested on suspicion of going onto area adjacent to playing area contrary to the Football (Offences) Act 1991, remains in police custody.
"Officers are investigating circumstances to establish whether any criminal offences have been committed."
Wenger, in his 19th season at Arsenal, was the subject of protests by some Gunners' fans earlier this season, with a banner asking him to leave unveiled at West Brom in November.
A solid recent run of form has dampened criticism of the Frenchman, who guided his side to the FA Cup in May, a first trophy in nine seasons.
But his side lost for the first time in five matches at Southampton as Ronald Koeman's side capitalised on two errors by Arsenal goalkeeper Wojciech Szczesny to move fourth in the Premier League, one place and three points above their visitors.