The former Aberdeen star was crocked during Thistle's abandoned SPFL Premiership clash with St Johnstone last month and went under the knife yesterday in a bid to repair the damage and speed up his recovery.
Osbourne was arguably the Jags' stand-out performer in the opening weeks of the campaign and has become a firm favourite with the Firhill fans since making the switch from the Dons this summer.
But Thistle are now preparing for life without the midfielder after the bombshell news.
Archibald said: "I think he is going to miss the whole season.
"He got his operation yesterday and it is looking like he will miss the rest of the season.
"It is a big blow for us. Once the specialist saw his scan, we thought he might be back after three months and we would have him for the run-in, but it is looking now that it is very unlikely that he will be back."
Having seen one of his key men ruled out for the rest of the campaign, Archibald is eager to bolster his depleted ranks in the transfer window this month.
Striker Lyle Taylor has already made the move to Firhill after penning a loan deal from English League One side Sheffield United.
But with Stuart Bannigan facing a two-game suspension, skipper Sean Welsh on the sidelines and Hugh Murray leaving the club on Monday, a central midfielder is now one of his priorities.
He said: "It was an area we were well covered in at the start of the season and up until four weeks ago it wasn't an area we were looking to strengthen.
"With Gary Fraser going back to Bolton, Osbourne out and Bannigan suspended, we are light on bodies in there.
"We are trying everything we can (to get Gary back).
"He is down there for a chat with Bolton and we are waiting for an answer."
Another player who is on Archibald's radar is Celtic youngster Dylan McGeouch.
As exclusively revealed in SportTimes, the Parkhead kid is one of the names on Thistle's list of targets this month.
And the Jags boss has confirmed the Scotland Under-21 star is a possible recruit.
He said: "Dylan was on a list of players we thought would add quality but we've not contacted Celtic or taken it any further.
"It's something we are aware of but I think he's injured just now so that's why we left it. But we could quite possibly return to it.'
After ending their long winless run with victory over Hearts last weekend, Thistle head into a crucial three-game Firhill run against Ross County, St Johnstone and Kilmarnock in high spirits.
But Archibald has criticised the SPFL's decision to reschedule the postponed Saints game for next midweek.
He said: "We have three home games in quick succession.
"It's frustrating because we could have done with putting the St Johnstone game back.
"But I think the league want us to play it as early as we can.
"We didn't try to get the St Johnstone game put back.
"The league came to us with a couple of dates but it was hard to get it when we wanted it because they are in a both cups."