Alan Shearer's career could be over after the Newcastle skipper suffered suspected knee ligament damage in the derby victory at Sunderland.
The 35-year-old had fired his side ahead with a 61st-minute penalty, his 206th goal for the club, when he was hurt in a challenge with substitute Julio Arca.
He tried to play on, but limped from the pitch at the Stadium of Light to be replaced by Albert Luque with 19 minutes remaining.
Caretaker manager Glenn Roeder later admitted there is real concern Shearer might not play in the remaining three Barclays Premiership fixtures of his final season, which will be followed by his testimonial on May 11.
'There is real concern that he has a ligament injury, and with the season running down now, that he might not be fit before the end of the season,' he said.
'I hope so much that is not the truth and it won't work out that way, but we are really concerned.
'He's had a brace put on his knee. It was the body-weight of the man who fell on top of him that his knee couldn't take and over-stretched the ligament.
'Tomorrow, the doctors will have a look at it, a close look, and see how much swelling there is there and lack of movement.
'It will certainly be scanned and once we see the scan, I suppose there will be a decision and an opinion given on whether he's got any chance of playing in these last few weeks of the season.
'But I'll remain positive there is a chance we will still get him back on the pitch, maybe in the very last game of the season.
'I didn't really get a chance to see Alan too much in the dressing room afterwards, but he was lying on the table there looking pretty despondent, of course.
'But he was so happy with the result, he forgot his own problem for a few minutes, and he made sure he congratulated every single of our players on what was a remarkable turn-around.'
Shearer's strike at the Stadium of Light - his first at the ground in club colours - was his 206th for Newcastle and the 409th of his senior career for Southampton, Blackburn, the Magpies and England.
'Alan Shearer was summed up in the two seconds before we could get him off the pitch,' said Roeder.
'He was hobbling with what looks like potentially a bad ligament injury and a Sunderland player was carrying the ball forward and he turned around and tried to make a tackle where most players would have been lying on the floor curled up.
'That just sums up Alan and why he's had the career he's had and why he's the person he is. It's a shame they don't make more people like that.'
Shearer's injury overshadowed a remarkable game in which the Black Cats, still looking for a first home Premiership win of the season, dominated for almost an hour.
Justin Hoyte fired them ahead with the first goal of his loan spell from Arsenal with 32 minutes gone, and the Wearsiders remained in the driving seat until the arrival of substitute Michael Chopra.
The newcomer announced himself with his own opening league goal within 13 seconds, profiting from hesitation between Steve Caldwell and goalkeeper Kelvin Davis.
Hoyte's tug on Charles N'Zogbia gave Shearer the chance to make it 2-1 from the penalty spot, then N'Zogbia wrapped up the points with a third after 66 minutes.
By the time Albert Luque broke his goalscoring duck for Newcastle two minutes from time, many of the home fans among a crowd of 40.032 had already left.
'For 90 minutes on Friday (at Manchester United) and for 60 minutes up until they scored their first goal today, you saw a real progression in the way we played and the way we moved the ball,' said caretaker Sunderland boss Kevin Ball.
'Everything about them was what I wanted. I said to the players before the game, `In life you get moments and make memories - make today one of those days'.
'Unfortunately from the first goal onwards, they have made a memory of the wrong sort.
'The way we conceded the goals hurts the most because, with the utmost respect to Newcastle, I feel we beat ourselves today as opposed to Newcastle beating us.'
Newcastle have three games left this season, with Shearer set to retire at the end of the campaign. Should he fail to return his last goal will be a strike against his side's bitter rivals.
'It's a great way to go out if it is,' he said on Sky Sports News.
'I've been waiting five or six years for a penalty against this lot because I missed my last one against Sunderland, and the wait was worthwhile.
'There was a lot of frustration and anger in that penalty.'
He added: 'It was a tremendous turnaround from us because we were rubbish in the first half and the manager has come in and let us know what he expected from us.
'To be fair to the boys they've delivered that in style.'