Orient manager Russell Slade conceded it was going to be "very difficult" for Orient to finish in the top six following their 2-1 defeat at Exeter.
Exeter striker Jamie Cureton struck in each half to take his season's tally to 19, while Dean Cox fired a spectacular equaliser for Orient. The victory takes Exeter level on 61 points with Orient and leaves them five points adrift of the final play-off place with four games remaining.
Slade said: "I thought our performance was patchy. Exeter got out the blocks a lot quicker than us and not only did they go 1-0 up, but they could have gone 2-0 up at that particular time.
"But we had one man on our side that was in great form - particularly in the first half - and that was Dean Cox.
"He scored with a fantastic finish and was so unlucky not to put us in front when his shot has hit the outside of the post, and then there was a chance that went right over Harry Kane's foot, so we ground it out and got ourselves back into the game.
"We need to get back to winning ways. In terms of a play-off shout, I think it's going to be very difficult. You have to look at the recent form we are in and the form we are in is not a good trend. We need to alter that momentum, but I believe we can do that."