Jim Mallinder has confirmed that injured prop Alex Corbisiero will need surgery on his knee.
Corbisiero last played for Saints in a pre-season friendly against Worcester in October and has not played a competitive game this season.
The current injury is a big blow for Saints and the 27-year-old, who has made 30 appearances for the club since joining from London Irish in 2013.
And Mallinder said: “Corbisiero unfortunately will have to go in for another op on Tuesday so he’ll be out for a few more weeks.
“It’s just a bit of a clean-out operation so it’s not major.
“It’s not good for him but he’s being positive about it and so are we.
“The surgeon is positive he can sort him out so hopefully he’ll be back sooner rather than later.
“It is bad news for the squad having so many players injured, but it’s opportunities for other players.
“In those Waller boys, we’ve got two cracking local lads who are taking their opportunities.
“We swapped it round today and young Ethan started. He didn’t let himself down at all, so we’re very lucky to have that cover.”
Saints were without six forwards for the 13-11 win at Bath on Saturday, with Dylan Hartley, Courtney Lawes, Calum Clark, Tom Wood and Matti Williams also out.
Hartley and Williams have been recovering from concussion, while Lawes has a knee injury, Clark is out until the new year and Wood has a shoulder issue.
And when asked to give an update, Mallinder said: “Lawes is hopefully back next week. He’s back out running and we think he’ll be available.
“Hartley, Wood, not sure. Hopeful on those. Wood got a shoulder knock, Hartley recovering from his concussion.”