Dallas' playoff hopes took a big hit on Thursday. 

The Stars announced that defenseman Miro Heiskanen will be out indefinitely after being diagnosed with mononucleosis. 

The Stars currently sit in the second wild-card spot in the Western Conference, just one point over the Edmonton Oilers.

Heiskanen was on pace for a career-high 44 points in 78 games. The two-way defender signed a long-term extension worth $8.45 million until 2028-29 last July and has since proven the team made a good choice in locking him up long-term.