This time the ACL injury was in Smith's right knee. He needed a left knee reconstruction in August, 2015, after he was hurt in a VFL match but returned last season to play one senior game - the second of his AFL career.

For a club that overcame a dreadful run of injuries on their way to their drought-breaking premiership last year, another serious injury to a promising young player was a significant blow so early into their premiership defence.

"Obviously it's a lot of bad luck, but we'll support him and get him going again," Bulldogs coach Luke Beveridge said after Thursday's narrow pre-season loss to the Brisbane Lions.

"It's obviously hard to give him that message at the moment, but yeah, it's a bitter pill to swallow tonight.

"We won't dwell on it, as much as it's heart-breaking for Roarke, all of us and his family.

"We think Roarke has got a really bright future. He's had so much bad luck so early in his career."

The reigning premiers have less significant long-term injury concerns in their big-man division, with injured pair Jordan Roughead and Tom Campbell set to miss the first-round clash with Collingwood.

They were both missing from the team that lost to the Lions as the Bulldogs went in with just nine players from their premiership team.

"Tommy has rolled an ankle so we don't think he'll be available for round one. He's going to miss some training. He definitely won't play senior footy for a few weeks," Beveridge said.

"As far as recognised ruckmen, other role players, it's Tim (English) and it's Tommy Boyd. We've got to work out what the best combination is."

That combination for round one is likely to feature 205-centimetre big man English, the club's first-round draft pick who impressed against the Lions.

"I love the way that Tim English went about his work as a ruck and a forward," Beveridge said.

"He's definitely a really intelligent footballer who doesn't shirk that side of the game. I really liked his contribution in what's his first competitive senior match of footy. There's lots of encouraging signs.

"We've been forced into that situation where we need to work out what our ruck division looks like, when it comes to that round one game against Collingwood."

The Bulldogs also left out Marcus Bontempelli at the last minute after the young gun suffered a minor ankle injury at their pre-season camp in Queensland.

"He's been a bit ginger for a few weeks. But he was at the point where we thought he was going to play tonight, but in the end we didn't take the risk.

"Hopefully he's right for the next one. Time will tell."