Long has hit four goals for the Royals this season but was guilty of missing a host of chances in the 0-0 draw with Coventry on Saturday.
McDermott told the Bracknell Forest Standard: "I just say to him, do the right things. I keep faith with players who are putting themselves on the line for the club, and that's what he's doing.
"He's getting in the right areas and he's got to keep doing that. He's got to make sure nothing gets in his head. We'll give him as much support as we can, as we do with all the strikers, anybody in our team.
"What would affect him would be people getting onto him, but he doesn't get that in our dressing room and he doesn't get that from me. He's still young, 23 years old, and he'll be taking the opportunities soon I am sure."
Source: PA
Source: PA