Mumford was a late withdrawal from the Giants clash with the Western Bulldogs at StarTrack Oval, with the club citing general soreness for his absence.
But GWS coach Leon Cameron said after the Giants' 27-point loss that Mumford had undergone a minor operation during the match.
Five talking points: Greater Western Sydney v Western Bulldogs
"We thought it was just general soreness. Unfortunately, with 'Mummy' he had a very sore knee and he had a very sore shoulder," Cameron said.
"But his knee's really blown up and he's been operated on today actually, so we had to pull him out late.
"It's a very, very minor operation, so he's probably going to miss one or two weeks.
"His knee just blew up and they just didn't want it to get infected. They flushed it out … and it was only really late that it happened, when we were playing."
The Giants' injury woes only got worse on Saturday, with Will Hoskin-Elliott subbed from the game after Dogs defender Dale Morris tripped him with his leg in the first quarter.
Morris appeared to make contact low on Hoskin-Elliott's left leg.
Cameron said he had not seen the incident that is likely to be scrutinised by the Match Review Panel, but said Hoskin-Elliott could miss the Giants' clash with Adelaide next week.
"It's probably a very significant cork. I don't think it's anything other than that, but whether or not he's right for next week or he comes in the week after that, (I don't know)," Cameron said.
"It was disappointing because he was sub last week and he wanted an opportunity this week and he got one and unfortunately got injured."
Defender Josh Hunt also left the field late in the game after appearing to injure his knee landing awkwardly following a marking contest.
But Cameron said he believed Hunt had merely suffered a "corky".
Cameron was pleased with the Giants' first half against the Dogs, particularly the first quarter when they kicked five goals to get out to a 26-point quarter-time lead.
But he felt the Bulldogs started to get on top early in the third quarter and his young team just wasn't able to halt their momentum.
"I thought our first half was good, some good quality footy," Cameron said.
"Having 21 inside 50s in the first quarter and not capitalising and putting more scoreboard pressure (on them) probably came back to haunt us a little bit.
"I thought their ball use was better than ours, especially after half-time.
"We were starting to get concerned about seven or eight minutes into the third quarter. They started to use the ball really well and cut us up through the middle of the ground a couple of times."
Twitter: @AFL_Nick.
"We thought it was just general soreness. Unfortunately, with 'Mummy' he had a very sore knee and he had a very sore shoulder," Cameron said.
"But his knee's really blown up and he's been operated on today actually, so we had to pull him out late.
"It's a very, very minor operation, so he's probably going to miss one or two weeks.
"His knee just blew up and they just didn't want it to get infected. They flushed it out … and it was only really late that it happened, when we were playing."
The Giants' injury woes only got worse on Saturday, with Will Hoskin-Elliott subbed from the game after Dogs defender Dale Morris tripped him with his leg in the first quarter.
Morris appeared to make contact low on Hoskin-Elliott's left leg.
Cameron said he had not seen the incident that is likely to be scrutinised by the Match Review Panel, but said Hoskin-Elliott could miss the Giants' clash with Adelaide next week.
"It's probably a very significant cork. I don't think it's anything other than that, but whether or not he's right for next week or he comes in the week after that, (I don't know)," Cameron said.
"It was disappointing because he was sub last week and he wanted an opportunity this week and he got one and unfortunately got injured."
Defender Josh Hunt also left the field late in the game after appearing to injure his knee landing awkwardly following a marking contest.
But Cameron said he believed Hunt had merely suffered a "corky".
Cameron was pleased with the Giants' first half against the Dogs, particularly the first quarter when they kicked five goals to get out to a 26-point quarter-time lead.
But he felt the Bulldogs started to get on top early in the third quarter and his young team just wasn't able to halt their momentum.
"I thought our first half was good, some good quality footy," Cameron said.
"Having 21 inside 50s in the first quarter and not capitalising and putting more scoreboard pressure (on them) probably came back to haunt us a little bit.
"I thought their ball use was better than ours, especially after half-time.
"We were starting to get concerned about seven or eight minutes into the third quarter. They started to use the ball really well and cut us up through the middle of the ground a couple of times."
Twitter: @AFL_Nick.
