Chris Chester expects disciplinary action against Wigan Warriors
Winger Johnstone, who scored two tries in the opening round against Leeds, left the action in the 19th minute with a head injury and didn't return.
Willie Isa was involved in the tackle and though no Wigan player was punished, Chester expects the RFL's match review panel to issue charges when it scrutinises the game on Monday.
"Losing Tom Johnstone to a high shot didn't help (and) they executed some decent plays down our left edge," said ex-Warriors player Chester.
"Tom is a bit dazed, I thought there was something in it to be done, there and then. It was let go, and we lose a player off the back of foul play... I'm not sure how that's not been picked up when we have plenty of guys watching the game in the stand. But somebody will benefit from it next week.
"It's contact on the head, and they've shown it three or four times on Sky, I don't know how it's not been picked up. But that's not lost us the game - our intent in the second-half, and not playing tough enough for long enough, lost us the game. But with so many camera angles I don't know how something like that goes unpunished."
Adrian Lam, though, seemed unconcerned about any repercussions.
"I don't think so, the referees had an opportunity to put it on report and give a penalty (and didn't)," he said. "From what I saw it wasn't that bad."
Wakefield were level 6-6 at the break but went down 34-6 after leaking five unanswered tries.
Chester added: "We had some good control in the first 40 minutes, we dominated field position and we really struggled with out end of sets. We're in bother when we've got Joe Westerman and David Fifita kicking."We didn't match the energy Wigan came at in the second half. We didn't have any calm heads tonight."