Wimbledon officials are today set to probe the incident which saw Romanian Victor Hanescu apparently spit towards the crowd before quitting his third-round men's singles match.
Hanescu had won the opening two sets on tie-breaks yesterday, and had match points in the third. But a tie-break went against him and German opponent Daniel Brands then levelled the Court 18 match by taking the fourth set 6-3.
Hanescu fell behind in the deciding set before the apparent spitting incident, which was followed by the 28-year-old from Bucharest opting to retire from the match, citing a leg injury.
Four spectators were arrested on Court 18 but an All England Club spokesman claimed the spitting incident and the arrests were not linked.
The club spokesman said: "The initial thought was that the four people arrested were part of the same spitting incident. But the thinking now is that possibly they weren't. That was just a random coincidence.
"Therefore this alleged spitting incident is directed at a different person or people who we don't know."
A spokesman for the Association of Tennis Professionals, who run the men's game, said there would be no comment from the organisation until after grand slam supervisors and referees meet this morning, as they do each day, to discuss disciplinary matters.
Hanescu was struggling with injury during the latter part of the match and received on-court treatment.
A Scotland Yard spokeswoman had earlier said four men were being questioned under the Public Order Act after Hanescu complained to officers.
The spokeswoman said: "Police were called to Court 18 following a disturbance.
"Four youths were arrested. They have all been taken to a south London station under Section 5 of the Public Order Act."
Hanescu could face severe punishment from tournament officials.
The All England Club spokesman confirmed: "The umpire has seen it (the spitting incident), if that's what it was.
"The umpire issued a code violation for unsportsmanlike conduct that covers things like spitting and swearing.
"His report will obviously be considered along with any other witnesses that we have from our side and then the referee will obviously look at those and any other footage he's got available to him with his colleagues, and at some stage will make a decision on what should or should not happen."
A standard offence of unsportsmanlike conduct carries a maximum fine of $10,000 (€8,087).
Under Grand Slam rules, any act deemed to be "flagrant and particularly injurious to the success of a tournament" can be judged as a "major offence of aggravated behaviour".
In 1995, the American Jeff Tarango had a row with umpire Bruno Rebeuh at Wimbledon and refused to play on, and was handed a ban which ruled him out of the following year's Championships.
Court 18 had already hosted the most dramatic scenes at the All England Club this year as John Isner and Nicolas Mahut served up the longest game in tennis history.