The Red Devils’ last two Super League fixtures, against Wakefield and Hull, were postponed and Marshall says the club are still suffering from the after-effects of five players returning positive tests.
“We’ve got five players positive and around 10 or 11 isolating,” Marshall said at his weekly press conference. “We’ve had seven players in training today.
“We’re not on our own, there’s a lot of clubs in the same position. We’re hopeful the guys in isolation will be out on Friday and back in training.
“We’re not going to make any excuses though, we’ll be fielding a team on Sunday to beat Castleford.”
Earlier this week, the Red Devils announced that half-back Chris Atkin has signed a two-year contract extension with the club, with the option for a third year.
The 28-year-old joined the Red Devils from Hull KR ahead of the 2020 season and has played in 10 of their 13 league and cup games so far this year.
Marshall said: “I’m really pleased to see Chris pen a new deal with us. He’s a quality player and a brilliant individual off the field.
“He’s been one of our most improved players this year and has really bought into our plans and the direction that our club is heading.”
Atkin said: “It was an easy decision to make when I sat down with the club.
“Salford has quickly become my home since I arrived here last year and everyone at Salford has always made me feel welcome and valued, our loyal fans included.
“I’ve enjoyed my time here so far. We’ve got a brilliant set-up at Salford and I’m really looking forward to the future.”