The luckless wideman has suffered a torn ACL for the second time in just two years and will miss the rest of the season.
Chester has received better news on Dream Team centre Bill Tupou who also injured a knee in Friday’s win at Hull FC.
He will miss Thursday’s televised home game against Warrington Wolves but could be back for the following week’s contest against Salford Red Devils.
“Bill’s is nothing long-term,” said Chester.
“We were all fearing the worst when they both got on the bus with a knee brace and crutches.
“To lose two guys like that - Bill and Tom - who regularly get 130 to 150m per game, they’re going to be hard shoes to fill.
“But it gives someone like Joe Arundel an opportunity and we have a little bit of cover there as well with some young kids while there’s potential as well to go into the loan market or have a look and see what’s available.”
Trinity full-back Ryan Hampshire had a successful spell on the wing with Castleford Tigers in 2016 but he is currently impressing in the No1 role.
Chester says he will speak to chief executive Michael Carter and chairman John Minards after the game against Warrington.
“I said to Michael if we get one more injury in the outside backs we’re in a bit of strife,” he conceded.“Last year we had a little bit more depth with Mason Caton-Brown (who then left for Toronto)
“This year we’ve got young Lee Kershaw, we have Rocky (Hampshire) as well that can play there but we don’t really want to disrupt something that’s going well already just for the sake of filling one position.
“We’ve had a few names thrown at us but we’ll wait and see what happens Thursday. “We’ll know more about Bill over the next 24/48 hours and then I’ll sit down with Michael and John to see what we can bring in and what quality is out there.
“It has to be the right fit for the club as well.”
On how Johnstone is bearing up, Chester added: “He’s in good spirits.
“It didn't come as a shock this time whereas the time before when he did his ACL in the Catalans game in 2017 he thought he’d just jarred his knee or got a strain to his medial.
“That did come as a shock but Friday night he was in so much pain he knew something serious had happened.
“He’s disappointed and fed up but he’s got a good family behind him and the support of the club, staff and players and everyone is just really disappointed for him.
“He’d started the season really strong and was playing particularly well on Friday night as well causing Hull some problems."
Wakefield will welcome back prop George King against his former club Warrington after he was left out at Hull for tactical reasons.