UEFA will take Rangers' previous conduct into account when deciding whether to take any action.
The club have been fined twice in the last four seasons by European football's governing body over the behaviour of their fans and manager Smith is worried the next sanction could be even more severe.
"Obviously, we have received warnings before and it will be hugely disappointing if it does impact on the footballing side of things," he said.
"I'm not currently aware of the whole background of the situation. So whether you're critical of the supporters or critical of the policing and the stewards. it is left up to you.
"But it is a situation Rangers have been in before and we can't run away from the fact.
"If it does impact and the consequences mean we do have to miss European games then that would be an enormous blow for the club. I have no indication as to what UEFA are proposing but the thing Rangers can't run away from is it's not an isolated incident."
Pressed further on the impact any European ban would have on Rangers, who are facing financial troubles at present, Smith added: "In the current climate, it's the last thing the club needs. European football is important to this club."
Although condemning the minority of fans involved in Wednesday's trouble, chief executive Martin Bain insists it was triggered by poor organisation at the Steaua Stadium and over-zealous policing, and has vowed to argue a strong case.
Bain's explanation was also backed by Superintendent Mike Dean of Strathclyde Police, who was helping to co-ordinate security at the ground on the night.
UEFA appear to have taken this into account after also beginning disciplinary proceedings against Unirea over a "lack of organisation" regarding the entry procedure for spectators at the ground.
But that may not spare Rangers punishment after television pictures showed a number of travelling fans clashing with Romanian police in the stands during half-time, while one supporter was seen to rip out a seat.
Police used CS gas spray in an effort to disperse supporters.
In recent years, the Light Blues were fined £13,300 for fans' discriminatory chanting and £9,000 after supporters attacked their opponents' team bus during an away game against Villarreal in 2006.
The following year, they were fined £8,280 on an improper conduct charge for fans' behaviour at an away UEFA Cup game against Osasuna.
Supporters have also been in trouble with police, with the rioting during last year's UEFA Cup final in Manchester regarded as one of the most shameful episodes in the club's recent history.