Platt was forced off during the recent defeat at Hull FC following a tackle on former Bulls team-mate Jason Crookes which led to him suffering concussion but also a medial collateral ligament injury to his knee.
The winger is now expected to be missing for up to three months, dealing a major setback to the Bulls after Langley and Walker sustained knocks during Saturday’s 38-12 win over Castleford.
Langley picked up a groin injury which could rule him out for up to three weeks and Walker suffered a damaged bicep which requires further assessment, leaving Cummins facing a nervous wait ahead of this weekend’s home clash with St Helens.
Bulls physio Dan Ramsden said: “Platty has an MCL tear and could be out for up to 12 weeks. This occurred in the same tackle in which he was knocked out at Hull FC.
“Langers has a groin strain which means he could be out for two to three weeks, while Chev suffered an injury to his bicep which will need further assessment.”
The Bulls are currently without Luke Gale, John Bateman and Ben Evans as they recover from injury.
And prop Nick Scruton faces a nervous wait to see if he will be called before the RFL’s match review panel after catching Castleford half-back Gareth O’Brien late during Saturday’s win.
O’Brien, on loan from Warrington, required treatment and was forced off but returned to the action in the second half.
The injury woes aside, the Bulls claimed an ultimately comfortable victory over Ian Millward’s men.
Home-grown second-rower Jobe Murphy made his debut off the bench in the second half but full back Brett Kearney was the star of the show with a superb hat-trick.
Despite scoring six tries and running out emphatic victors, Cummins called for an improvement in attack heading into the St Helens match.
“It’s good that we’re playing St Helens now because we know we’re going to have to be miles better than we were against Cas,” said the Bulls coach.
“I liked the way we dug in and helped each other but you’ve got to ask more questions of a team like Saints.
“That will focus the boys a little more in training and make sure that we deliver what we practice.”
Murphy, 20, conceded a number of penalties as his enthusiasm got the better of him.
But Cummins said: “I’m just glad that Jobe’s had the opportunity to play first-team rugby because that lad has been through hell these last few years. He will settle down and continue to improve.”
Kearney feels the Bulls have plenty to work on this week as they bid to get the better of Saints.
The Aussie, who took his try tally for the season to five, said: “We’re still off the mark a little.
“We put them under pressure early and should have got over the try line a few more times but we dug in deep and when our opportunities came again we took them.
“We’ve got a lot of work to do with our attack there. We can put teams to the sword a lot earlier than we are at the moment.
“A key thing about the Saints game is that we’re at home again and we want to have a good record here.
“Saints have been a top team for the last ten years now and we’ll have to improve on what we did against Castleford.”