The midfielder was stretchered off during relegation-threatened Newcastle United’s shocking 3-0 defeat to Brighton and Hove Albion at the Amex Stadium last night.
Hayden had been accidentally caught by midfielder Yves Bissouma, who checked on him after the game.
There are fears that the 25-year-old’s season could be over, and Bruce admitted that the injury “didn’t look good” after the defeat, which led to calls for United’s head coach to be sacked.
"It’s a knee injury,” said head coach Bruce, who retains the backing of owner Mike Ashley despite a run of just two wins from 20 games in all competitions. “We don’t know the severity until obviously he has scans and x-rays, but it doesn’t look too good, that’s for sure.”
Hayden tweeted a message to Bissouma – and United’s fans – after the game. Bissmoua had immediately shown his concern for Hayden after their clash before the break.
He said: “Gutted all round is an understatement! I will be doing my utmost to recover as quickly as I can from this injury to help the team. Respect to Bissouma for checking on me after the game. Was a complete accident, and (thanks to) Brighton medical staff for their help tonight also.”
Newcastle remain two points above the relegation zone following the Brighton game. The 17th-placed club’s next game, which follows a two-week international break, is against Tottenham Hotspur at St James’s Park on April 4.