A group of approximately 100 men approached the Green Man pub at 17:50pm BST wearing England hats and scarves, but it is believed that they were in fact German.
The group, which included many who were wearing masks, started to attack England supporters in the beer garden of the pub, with the disorder lasting for around two minutes.
A least three people sustained serious leg, wrist and thumb injuries, while a 'number of people' suffered head and facial injuries.
A statement read: "At 17:50hrs on Monday, 26 September a group of approximately 100 males, many wearing masks, approached a pub in Dagmar Avenue, Wembley through an alley leading towards the car park.
"While a number of the group were wearing England hats and scarves, it is believed they were German 'fans'.
"The group entered the beer garden of the pub and began assaulting customers, most of whom were in the area to attend the England vs Germany match. Punches and projectiles including traffic cones were thrown.
"Officers responded and the group fled. The disorder lasted for around two minutes.
"A number of people sustained head and facial injuries. We are also aware of three people with serious leg, wrist and thumb injuries. None of those injured are believed to be in a life-threatening condition.
"There have been four arrests so far in relation to the disorder."
Meanwhile, Luke Robinson - an eyewitness who visited the pub with his son before kickoff - claims that the mass brawl lasted longer than the two minutes the Metropolitan Police have stated, and he revealed that he has "never seen it like that" having previously visited the pub regularly for England matches.
Speaking to i, Robinson said: "There's an entrance at the back of the Green Man and about 50 of them turned up wearing masks and England scarves.
"They stormed in, were hitting anyone and everyone. It was going on for a good five minutes before the police arrived.
"A lot of people were in a bad way. People were on the floor, unconscious, covered in blood. Even kids — one lad no older than 13 had a bleeding nose. One guy was with the paramedics and still unconscious when we left.
"It's the main England pub. I've never seen it like that before and I come to every home game. We were there when England played Germany in the Euros and when there was all the trouble around the final, but this is the first time I've seen it like it."
England concluded their Nations League campaign without a single victory from their six matches in League A Group 3 after playing out a thrilling 3-3 draw with Germany.
Premier League duo Ilkay Gundogan and Kai Havertz put the visitors two goals in front before strikes from Luke Shaw, Mason Mount and Harry Kane turned the game on its head for the Three Lions, but Havertz netted an 87th-minute equaliser to force both sides to share the spoils.