Merson, who has just completed 12 months at Villa Park after his pounds 6.75m move from Middlesbrough, played a key role in Villa's last home League match, against Bradford, after coming off the bench.
The former Arsenal player, whose struggle with drug and gambling addictions has been well documented, is desperate to hold down a regular place in the side. But Merson fears Gregory may view him as being most effective in a bit-part role - and is resigned to turning out for the reserves against Middlesbrough tonight, rather than starting the Premiership match against Liverpool this weekend.
Merson said: "I came on as a sub against Bradford and Chester [in the Worthington Cup] and did OK, but I'm frightened that's the situation and role I could get into all the time.
"That's the thing that worries me, that being a sub could start to become my regular position and viewed as my best role because I've done so well coming on.
"The boss might look at it and think: `I've got to put a team out that might win - but if we don't look like doing that then I've got someone, Paul Merson, to fall back on to turn the game'.
"He might also be thinking `If I play Paul Merson from the start and things aren't working then what and who do we fall back on to turn things around?'
"I want to play regularly but I don't think I've got half a chance of playing on Saturday against Liverpool. I am being realistic. You get vibes and feelings about things, and that's one of them.
"There is a lot of added pressure on me to perform if I play, but I don't mind that. I know I can play, but it upsets me when I don't perform or I'm not given the reins to perform."
Merson, nevertheless, does admit that he presents Gregory with a dilemma when it comes to picking his team. He said: "The manager is in a position at the moment where he can pick a team without me that is very solid but won't make a million chances. For a team in the top seven I don't think we've made 25 chances in eight games. If he goes the other way and plays me, we will make chances and I'll be the one that creates stuff. But we are not going to be as solid going the other way because I'm not an Ian Taylor. I won't get around the pitch, breaking the game up and tackling.
"It hurts me when I don't play, but I do understand it's a funny situation and the manager is thinking: `can I play him in that system?'
"But I know if I play and play well that we have got more than a 50-50 chance of winning."
n Middlesbrough are facing a midfield injury crisis ahead of Sunday's derby match against Newcastle. Paul Ince and Juninho are both doubtful for the game after picking up injuries in the 1-0 defeat by Chelsea last Saturday.