Hegeler was substituted after 24 minutes of Leverkusen's 1-1 draw with Hannover on Saturday, their fifth straight game without a win in all competitions, and tests have revealed an ankle ligament tear.
The 26-year-old midfielder has made 26 appearances for Sami Hyypia's side this season, but Leverkusen expect him to be sidelined for the remainder of the campaign.
"The midfielder has suffered a tear of the anterior ligament in his right ankle and is therefore likely to be out for the rest of the season," the club confirmed on their official website.
"On Sunday morning, an MRI scan brought the sobering diagnosis. He is expected to have surgery on his ankle as early as Monday."
Leverkusen grip on a top-three position in the Bundesliga is under severe threat after Schalke drew level with them in third with a 4-0 win over Hoffenheim on Saturday.
