It's bad enough that the slumping Boston Celtics face another must-win situation Friday night against the Detroit Pistons.

What's worse is that Boston's starting backcourt of Dennis Johnson and Danny Ainge may not be completely healthy for Game Six of the Eastern Conference Finals.Detroit leads the series, 3-2. If the Pistons win Friday night, they will advance to the NBA finals for the first time. If the Celtics win, the seventh and deciding game will be played Sunday in Boston Garden.

Johnson and Ainge are suffering from strained lower backs as results of falls Wednesday night in Boston's 102-96 overtime loss. They were not required to attend Thursday's light workout at Hellenic College and did not fly to Detroit Thursday night with the team. They were scheduled to be examined this morning and, if all right, to leave at midday for Motown.

Johnson, who crashed to the floor several times Wednesday night, was injured with 3:13 left in the fourth quarter when he followed his own missed jumper with an off-balance shot. Johnson made the basket and fell flat on his back atop Bill Laimbeer, who had hit the deck before him.

Johnson grimaced immediately and rolled over. He struggled to get up and finally hobbled to the other end of the court. The Celtics committed a foul and called a timeout so Johnson could be assisted to the bench. When play resumed, he was back in the lineup. But when the game was over, he needed his wife's help to leave the Garden.

Nobody was sure when Ainge strained his back, but he also hobbled home Wednesday night.

Coach K.C. Jones, Mr. Pessimism when it comes to injuries, was concerned.

"They both look bad. As to the severity, if they're both still in bed, that's not very good. We'll know tomorrow if either one is coming or either one is playing," Jones said.

Trainer Ed Lacerte was more optimistic that the pair would be in uniform Friday night.

"If Game Seven were (hursday night), they would be out there," Lacerte said. He mentioned that the injuries were of "equal magnitude" and that he knew Wednesday night that both players were hurt.

Jones said he had not considered who would play if Johnson and Ainge are not available.

"I have not made any plans yet. Who knows? I might have to suit up," the former guard said.

Jim Paxson, Dirk Minniefield and Reggie Lewis are the candidates. And Larry Bird can play in the backcourt.

If Johnson and Ainge do play, Jones wonders how effective they will be.

"It's going to be tougher with the condition of our two guards," Jones said. "If they do perform, it will be under very difficult circumstances."

Johnson played a gutsy 49 minutes in Game Five. He scored 23 points, handed out eight assists, grabbed four rebounds and blocked a shot. He was the only Celtic whose play merited a star.