Lahm failed to see the funny side with the prank having generated plenty of free publicity for the start-up.
A Munich-based fitness start-up issued a grovelling apology to the World Cup winner over a fake April 1 story, which hit the German media last Saturday, falsely claiming he had invested in them.
The story even contained a fake quote attributed to the Bayern Munich star after an employee decided to circulate an internal newsletter to the German media without the knowledge of the company's bosses.
"It was an April Fool's joke which should have been sent exclusively to our members in a newsletter," explained the company's red-faced co-founder.
However, the stunt quickly backfired and although the firm apologised several times, Lahm failed to see the funny side with the prank having generated plenty of free publicity for the start-up.
"I'm taking advice and bringing the matter to the detailed attention of a lawyer," said the 33-year-old, who will retire from all football in June, in a statement.
"The personal apology reached me, but nevertheless, the company has overstepped the mark with this action.
"We will now get in direct contact and look for a solution."
The firm has already suggested making a donation to Lahm's charity, The Philipp Lahm Foundation, in an attempt to make amends.