The injury, a broken jaw, is expected to keep the 27-year-old out for the rest of the season.
The Australian was playing on a short-term deal with Saints, in the hope of putting himself in the shop window. The opportunity to impress potential employers has now been missed, however.
“It was unfortunate, Shannon did it in the first minute of the half, and stayed on the field,” Brown said.
“It was him making a tackle, and there was not much in it at all.
“It’s a tough game, isn’t it? We all keep saying that, as the years have gone on, the game’s got harder and harder.
“The collisions have got more frequent, and heavier, as the players have got bigger.
“Sometimes you have lucky runs, and sometimes you have unlucky runs. Unfortunately for Shannon, he’s a guy playing on very limited money, who’s looking to keep his career alive.
“He was doing a great job for us, and he was a player who I’d like to think if he wasn’t going to stay, that he’d get picked up somewhere else.
“Unfortunately what’s happened has taken him out of the shop window, at what could have been a key part of the year for him.”