Toronto has already seen Brazilian midfielder Jackson punished after the fact, receiving a one-game suspension and undisclosed fine for an elbow thrown off the ball in a March 22 win over D.C. United. Jackson received a yellow card on the play.
Nelsen is bracing for another possible intervention by the league's disciplinary committee in the wake of captain Steven Caldwell's studs-up tackle Saturday on Real Salt Lake midfielder Ned Grabavoy. Like Jackson, Caldwell was cautioned for the offence.
The Toronto manager says while safety of the player is paramount, he believes supplemental discipline levied when the offence was seen and acted upon by the referee during the game comes with a cost.
"When they start jumping in on the referees, it kind of undermines them a wee bit and kind of sets a precedent," Nelsen said Tuesday. "Because then when do they stop?
"Then every single thing that the referee has seen or hasn't seen can be jumped upon. I think it's a dangerous road to go on. Especially when the referee's seen it ... But it's up to MLS and it's up to the guys but hopefully they don't undermine the referee again."
Nelsen took a different approach when Jackson was awaiting word of his suspension.
While admitting Jackson should not have retaliated after being goaded by D.C. United midfielder Davy Arnaud, Nelsen then pointed the finger at Real Salt Lake forward Alvaro Saborio for his foul on A.J. DeLaGarza of the Los Angeles Galaxy the previous week.
"That could have broken his leg,'' Nelsen said of the Saborio challenge. "So if Jackson gets suspended, then you'd like to hope that a guy who's nearly broken a guy's leg is probably going to get suspended as well.
"But I don't know, you never know. I don't make those rules.''
With Real Salt Lake already suffering a glut of injuries at forward, it seemed pure gamesmanship by Nelsen. Saborio escaped further discipline, however.
Asked what sanction the Caldwell tackle merited, Nelsen said it was hard to say.
But soccer is a contact sport, he added, "and things are going to happen in a split-second.
"If you slow it down and you watch it 10, 20 times, every single tackle and every single play looks bad."
Nelsen said he had seen such supplemental discipline snowball during his playing days in England, with clubs constantly complaining about on-field transgressions.
Caldwell, meanwhile, said he just tried to win the ball.
"I've never been a dirty player, I've never had any problems with discipline in my career," said the hard-nosed Scot. "I've been sent off a few times but it's usually through endeavour and maybe last-man tackles.
"I've seen (the play) and it doesn't look good. But I went in to win the ball. My foot was low. It was definitely a booking. I take my booking, I accept my punishment. But I just see it as a guy going in trying to win the ball."
Caldwell's view is that the referee took care of the incident as needed on the field.
The disciplinary committee, however, can take further action in such cases if there is unanimous opinion that the play deserved a red card or was of "an egregious or reckless nature, such that the committee must act to protect player safety or the integrity of the game."
According to the league, the disciplinary committee's mission statement is "to preserve the integrity and reputation of the game and Major League Soccer, and to assist in ensuring player safety."