South African police Saturday launched an investigation of how an angry fan breached security and burst into England's locker room in Cape Town after their draw with Algeria.
The man in a red T-shirt was removed from the changing room, but was released without questioning, police spokesman Colonel Billy Jones said.
Guards were being questioned about why the man was let go, while police were examining security camera footage to try to find out how the man managed to get in, he added.
The English FA has made an official complaint to FIFA about the incident, which came after the team were booed off the field by many supporters following the woeful 0-0 draw.
"A fan got in past FIFA security, we've formally complained to FIFA after the game and will follow it up in writing. It is not acceptable. Thankfully there was no serious harm done," said an FA spokesman.
The incident is all the more sensitive given that Britain's Prince Harry and Prince William are reported to have visited the players in the dressing room earlier in the evening.
Security has been a chief concern for organisers ever since South Africa was named the World Cup host six years ago, with worries focusing mainly on the country's high crime rate.
But stadium security has moved to the fore as stewards at Cape Town and three other venues walked off the job last week in a pay dispute that forced police to take over security around the fields.
Protesting stewards twice clashed with police over the last week, once in Durban and once in Cape Town, as they tried to demand their salaries from Stallion Security, the firm that had been contracted by FIFA to screen fans entering the gates.
Police were also under pressure to crack down on illegal ticket sales Saturday, with Johannesburg's Saturday Star newspaper proclaiming "Ticket crooks rule" across its front page.
South Africa outlawed the resale of tickets just before the tournament started, meaning tickets can only be legally transferred through FIFA.
Scalpers can face a 15,000-rand (2,000-dollar, 1,500-euro) fine and up to five years in prison. A Nigerian man was slapped with a three-year sentence this week after he was found with 30 tickets that could not be verified.
Two men had their tickets for Friday's US-Slovenia match confiscated just before the game as they were apparently trying to sell them outside the stadium, police said.
But one officer at the gate to Ellis Park stadium in Johannesburg said police struggled to keep out scalpers, as fans desperate for tickets show up at the stadiums hoping to find a way in.
"We are trying to keep them away because it is illegal," he told the Sapa news agency. "But they are moving around all the time."
FIFA has cumbersome rules for reselling tickets, which can only be done online and not within three days of the match.
The world football body already drew flack for its online ticket sales system in a country where Internet access remains a luxury.
The threat of stiff penalties has not deterred scalpers from openly circulating around stadiums, and their numbers appear to be growing as the group stages advance and games become more critical to teams' hopes of making the next round.
Ahead of England's 0-0 draw with Algeria in Cape Town, one cheeky set of fans even jokingly offered to sell a young boy in exchange for four seats, carrying a placard reading "Child 4 Sale -- 4 Tickets".
Ten-year-old Josh Conlin was spared however when his 23-year-old cousin Jason Dodwell managed to acquire four at around double the box office price.