Newcastle Knights duo Andrew McCullough and Connor Watson will likely miss the rest of the season.

A horror day against the bottom-placed Bulldogs were compounded by serious injuries to first McCullough (hamstring) and then Watson (achilles).

Newcastle coach Adam O'Brien all but conceded that the pair will be out for the rest of the 2020 campaign.

McCullough could be on the sidelines for up to six months after his hamstring was "ripped from the bone" at MacDonald Jones Stadium.

It now seems likely the 30-year-old will take up the 2021 option in his favour with Brisbane, which per the terms of his mid-season release allows McCullough to return to the Broncos if he fails to land a 2021 NRL deal.

McCullough's unique contract situation ensures his short-term security. However, there is no promise his return home will see him take to the field, considering he left Brisbane after falling down the club's No. 9 pecking order.

It's still unclear what the terms of a return to Brisbane would look like, with board member and recruitment committee member Darren Lockyer confirming McCullough could be back at the Broncos on "a certain number of dollars" when he left in May.

The former Bronco's original four-year Brisbane contract was believed to have been worth around $500,000.

The Knights' 2021 salary cap is unlikely to have room to accommodate McCullough.

Watson, on the other hand, has been locked in negotiations with the Knights, with both parties keen on keeping the 24-year-old at the club.

However, Newcastle's salary cap situation will be under the spotlight as Tim Glasby's future remains uncertain, along with the impact of finals bonuses if they are to come into effect.

Rival clubs have asked about Watson's future, according to NRL.com, however have been told that the utility playmaker intends to stay with the Knights.

He is expected to go under the knife on Tuesday, and will spend an indefinite time on the sidelines.