Newcastle trail leading pair -- Arsenal and Manchester United -- by six points as the season enters its decisive stage, but that gap will be halved if they win at St James' Park on Saturday, with Arsenal playing in the FA Cup semi-finals on Sunday.
"Beat Manchester United and we are back in it," Shearer was quoted as saying in Newcastle's Evening Chronicle newspaper on Friday.
"Nobody knows just where we are going to finish in the premiership table. We have just got to keep on playing and if we beat Manchester United then things could be wide open again."
Newcastle manager Bobby Robson suggested their hopes of winning a first championship since 1927 were all but over after their controversial 2-1 defeat by Everton last weekend.
French full-back Olivier Bernard appeared to be fouled by Danish midfielder Thomas Gravesen just before Jonathan Woodgate gave away the decisive penalty at Goodison Park.
But Shearer said: "The most important thing is that we get back to winning ways. We have lost successive premiership games on only one occasion this season when Leeds and Chelsea beat us on the bounce
EXTRA IMPORTANCE
"It's not as though tomorrow's game with Manchester United wasn't already an important match but the Everton defeat has added to the importance.
"We are not worried about our form. In fact, we should get things into perspective. We have lost a game, and in controversial circumstances at that.
"Now we have....a massive game to get back into winning ways."
The former England captain has a total of 24 goals to his credit in all competitions this season but has failed to score in Newcastle's last three games.
The 32-year-old is not worried, however. "I would be a lot happier if we won 1-0 tomorrow and I didn't score than I was when I got my 100th premiership goal for Newcastle and we lost (5-3) at Old Trafford in November."
Robson said: "My advice (to supporters) would be to get there early and not to leave before the end. It will go off like a crackerjack and will go right to the end.
"Tomorrow is a massive game for both teams. If we win it will put us right back in there in terms of winning the title or finishing second.
"If we lose, we are out of it and will have to concentrate on finishing third."
