Lambie was not among the players released by the Springboks for round seven of domestic action, despite playing just 14 minutes in the past six weeks.
His last full match was in the Super Rugby final on August 4 followed by nine and five minutes in the Rugby Championship against Australia and New Zealand respectively.
"I think Pat Lambie is pretty desperate for some game time," Plumtree said.
"I think there might be one or two others like him as well … So it is a little bit frustrating but those are their [Springbok management] decisions."
The coastal team face the Lions in a top-of-the-table clash in Johannesburg on Saturday.
The Sharks have been boosted by the return of winger Lwazi Mvovo and hooker Craig Burden, who were both training on the Kings Park outfields on Tuesday.
"They always add value and Craig Burden and Lwazi are two great players," Plumtree said. "So it just gives us that little bit of extra depth."
The Sharks have a woeful recent record in Johannesburg, having not beaten the Gauteng team on their home turf in their last three visits.
They were twice ousted on the Highveld last year, including being trumped in the Currie Cup final, while they also lost in 2010.
"We know how tough the Lions are going to be," Plumtree said. "We haven't won up there for a long time now and they've found some really nice form … So we're going to have to be at our best and certainly a lot better than the last few times we visited their home ground. It's a really big game for us."
Plumtree felt the key to upsetting the Lions was to negate the effect of Elton Jantjies, the stand-out flyhalf in the competition to date.
"Elton's got a great skill-set," he said.
"He's a player that can play deep, he can play flat, he's kicking game is very accurate, he's goal-kicking is accurate … The Lions always play better when he's playing very well, so he's someone we'll have to make sure doesn't have a big game against us," Plumtree said.
"There have also been reports in recent weeks linking the young number 10 with a move to the Sharks next season."
Plumtree confirmed that talks were ongoing with the Lions, but stopped short of naming Jantjies as one of their targets.
"We have been talking to certain players from the Lions, but I'm not prepared to talk about who they are," he said.
There are no fresh injury concerns for the Sharks, and they have instead been boosted by the return of Steven Sykes. – Sapa