Long, who was sold for £6.5million after the Royals had failed to secure promotion to the Premier League, has proved a hit at the Hawthorns, scoring nine goals in 24 appearances this season.
"I speak to Shane regularly, he's a friend. The impact he's had since 18 years of age has been phenomenal," McDermott said.
"Sir Alex Ferguson mentioned him the other day and talked about what a top player he was and he knows what he's on about.
"He might end up at a top-four club, that wouldn't be beyond the realms of possibility.
"I remember when I first put him in the team he wasn't scoring but he was giving us so much. But then he started to score as well and he was phenomenal for us.
"He's exactly what we're about. You can say it in two words: Shane Long. I wanted him to stay but we couldn't afford to keep him. We had to sell to survive."