Viorel Moldovan, one of five Romanians booked in their 1-0 victory, went down in the penalty area as if poleaxed as players jostled for position at an Irish free-kick.
The Dutch referee, Mario van der Ende, missed the second-half incident as he tried to usher the Romanian defenders back. Television evidence was unclear although it showed Keane making an intimidating gesture with his forehead towards Moldovan's face.
The Romanian played on after treatment but was later substituted. The referee took no action against Keane, whose 48th-minute penalty was saved.
It is another trauma in Keane's controversial career. He was sent off for attacking a Russian player in Mick McCarthy's first match as manager last March. He was given a one-match suspension and then banned by McCarthy from Ireland's summer trip to America after failing to report for a friendly against Portugal in May last year. But he has played in all of Ireland's last five matches after making only sporadic appearances in the ill-fated Euro 96 qualifying campaign.
The incident with Moldova in the Republic's unlucky defeat on Wednesday night was just one of a series of unsavoury events. The Crystal Palace midfielder Ray Houghton was felled by a coin thrown from the crowd and played on with an ugly gash in his head. And the substitute Tony Cascarino complained afterwards that one of the Romanians spat in his face. Houghton did not need stitches but said: "I felt very wobbly for a while but just wanted to get on and finish the game."
The coin was thrown despite a warning over the public address system earlier when another missile, believed to be a plastic bottle, also landed on the pitch. Now Romania look certain to face severe punishment from Fifa.Reuse content