"Saab has started recruiting key personnel [from Kockums]," a defence source told The Local Germany on Monday.
Eight naval engineers have moved over to the Swedish military equipment makers, reported the Svenska Dagbladet (SvD) newspaper, which added that it was not yet clear what would happen with submarine production in the southern town Karlskrona.
The latest development follows tension last fall between Kockums' German owner ThyssenKrupp Marine Systems (TKMS) and the Swedish government, after TKMS shut Kockums out from its major market Singapore.
A defence source told The Local at the time that TKMS's purchase of Kockums had been a long-term strategy to kill off a rival on the market.
"The purchase of Kockums wasn't aimed at consolidating the naval industry and creating synergies, but at getting rid of a competitor," the German source said in October.
The same source said on Monday that the naval industry was awash with speculation that Saab was poaching staff in order to set up its own submarine unit.
Kockums and its predecessors have been building ships for the Swedish navy for centuries at the Karlskrona shipyard in southern Sweden, which now serves as the base of the company's Swedish operations.
Since 2005, however, Kockums has been owned by TKMS, which also owns German submarine maker HDW, a direct competitor to Kockums. In 2013, the German firm decreed that the Swedish shipbuilder officially change its corporate name to ThyssenKrupp Marine Systems, scrapping the Kockums brand name that has been a part of Swedish industry since the early 1800s.
Allan Widman, a Liberal Party (Folkpartiet) MP from Malmö and the party's defence policy spokesman, told The Local Sweden in October that he was "worried" about Kockums' future.
"Submarine building capabilities are essential for our armed forces and our ability to defend ourselves," he told The Local, adding that he had heard a number of "industry rumours" about the discord between TKMS and Kockums.
Additional reporting by David Landes, Stockholm, and Tom Bristow, Berlin.