The 30-year-old was told he had lymphoma and will now miss months of action as he undergoes treatment.
As a result, he will be absent for the start of the Bundesliga season, which will get underway on August 18.
But Gladbach have revealed that there is an "extremely high chance" that Laimer will beat the disease.
They went on to state that he could still return to football in positive news.
Gladbach's statement read: "Stefan Lainer will be missing from action for several months.
READ MORE SPORT STORIES
LeBron James issues update on son Bronny after cardiac arrest at USC training
Aston Villa hero questions Henderson's support for LGBTQ+ community following Saudi move
"After medical examinations, the 30-year-old right-back has been diagnosed with lymphoma.
"The Austria international will now need to undergo several months of treatment.
"The cancer has been detected extremely early and is treatable with medication.
"There is an extremely high chance that he will get back to full health, and a normal life including professional sport could still be possible."
Most read in Bundesliga
Footage shows former Klopp favourite airlifted to hospital after mountain bike crash
Liverpool transfer may have scuppered Man City's plans to land defender
Former Liverpool man Naby Keita out for 'several weeks' with injury sustained in warm-up
Harry Kane to be offered record salary with Tottenham contract expiring
Director of Sport Roland Virkus added: "We will do all we can to get Stevie the best possible treatment.
"We wish him and his family lots of strength and optimism in the fight against this disease."
Lainer has been with Gladbach for four years after joining from Red Bull Salzburg in 2019.
The Austria international made 18 appearances in all competitions for the Bundesliga side last season to help them finish 10th in the league.
Meanwhile he won four league titles during his time with Salzburg in his native country.
In total, he has made 125 appearances for Gladbach, scoring four goals and making 13 assists.
Lainer has also racked up 38 appearances for Austria's national team since making his debut in 2017.