Plowman, 20, underwent surgery in Sydney on Thursday night after falling awkwardly on his left elbow.
The operation went well with the GIANTS medical staff expecting Plowman to be sidelined for 12 weeks.
Plowman played 12 matches for the GIANTS in 2014 to take his career tally to 18 games.
Originally from Macedon in Victoria, Plowman was selected with pick 3 in the 2012 NAB AFL Draft and re-signed with the GIANTS last season until the end of 2016.
General Manager Football Graeme Allan said: “It’s disappointing for Lachie as he’s worked hard so far in the pre-season.
“But we’re very confident he’ll regain full fitness and make an impact in 2015.”
Young forward James Stewart is recovering well after suffering from glandular fever in December and is slowly building up his workload towards full fitness.
Stewart spent some time away from the club late last year and was on light training duties when the GIANTS went to the Sunshine Coast for a training camp prior to Christmas.
Having undergone knee reconstructions last year, defender Tim Mohr and key forward Jon Patton are both recovering well with Patton taking part in Monday’s 3km time trial at Tom Wills Oval.
Mohr looks set to return to the field in the early part of the season, while Patton is eyeing a return later in the season.
Small forward Liam Sumner remains sidelined due to a navicular stress fracture in his right foot and is expected to miss the start of the season while young recruit Jeremy Finlayson continues to recover from hip surgery and is expected to resume full training next month.
Another product of the PM CAPITAL GIANTS Academy, defender Zac Williams is also close to re-joining the main training group following a significant ankle injury at the end of the 2014 season.