Southend manager Paul Sturrock is facing an injury crisis.
Around seven or eight of those who played in Saturday's 1-0 first-leg defeat at Gresty Road are facing a race against time to prove their fitness.
Centre-back Mark Phillips (shoulder) is one of those affected having been forced off at the weekend although Sturrock is keeping his cards close to his chest regarding the identities of the others.
And he has had to put his fringe players on red alert for the showdown as the Shrimpers look to overturn Adam Dugdale's second-half header.
"At this minute in time we're not going to call ourselves Southend United, we're now going to call ourselves emergency ward 10," Sturrock told Blues Player on the club's official website.
"Seventy per cent of the team are up in the treatment room, all niggling knocks and everything else. I've told a lot of the players who have not been involved lately to at least put the game in their mind, make sure they appreciate they could be called upon big time. It will be right up until Wednesday before we know if a high percentage of our players will be fit or not."
Crewe will assess the fitness of midfielder Luke Murphy.
Murphy played a starring role as Alex secured a slender 1-0 advantage in Saturday's first leg at Gresty Road, but made way for Lee Bell in the closing stages due to some tightness in his groin.
"Murphy came through the game okay and we took him off in the last 10 minutes as a precaution as he had missed some training in the week," said boss Steve Davis. "We will check on him again and I'm sure he will be fine."
England Under-18 international Nick Powell took a knock to the ankle but is expected to be fit along with Carl Martin, who pulled up with cramp in his first outing for 12 games at the weekend.
One definite absentee is captain David Artell, who will be sidelined for up to eight weeks after suffering a broken metatarsal.