He was touted as one of the most important off-season additions for the Pittsburgh Steelers – but Aussie NFL star Cameron Johnston‘s campaign could already be over.

The 32-year-old former AFL prospect signed a three-year deal worth $13.46 million in March to become the team’s first-choice punter.

But in his debut for the franchise on Monday (AEST), Johnston was caught up in an ugly moment and now looks set for a lengthy stint on the sidelines.

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During the fourth quarter of Pittsburgh’s 18-10 win over the Falcons, Johnston punted the ball out of his own end, before being collected by an opposition player.

Steelers coach Mike Tomlin later revealed that the Geelong product could be gone for the rest of the season in a major blow.

“From a health standpoint, Cam Johnston appears to have a serious injury,” Tomlin said.

“I’ll have an update for you next time we come together. It’s a shame for him.

“This guy has been spectacular man through team development. He’s an absolute stud not only in his talents but his approach to business and so my heart goes out to him.”

All eyes were on quarterbacks Justin Fields and Kirk Cousins heading into their regular season debuts in new colours, but it was Steelers kicker Chris Boswell who starred.

The fan-favourite nailed six field goals – accounting for all 18 of his team’s points – while also filling in for Johnston late in the contest as a punter.

“I can’t say enough about Bos, not only in terms of him kicking the ball, but that punt was timely,” Tomlin said of his star kicker.

Pittsburgh were without first-choice quarterback Russell Wilson for the clash, but the performance of Fields could cast doubt over the veteran’s spot in the pecking order.