Teligent shares plunged $1.25, or 21 percent, to a 52-week low of $4.81 Monday after a pair of brokerage firms downgraded the wireless communications services provider.
Ferris Baker cut the stock from a "strong buy" rating to an "outperform" while BB&T Capital Markets slashed it from a "strong buy" to a "hold."
On Friday, PaineWebber clipped it from an "attractive" recommendation to "neutral."
Last quarter, Teligent posted a loss of $164.1 million, or $2.94 a share, on sales of $32.3 million.
First Call Corp. consensus expects it to lose $3 a share in its third quarter and $12.14 a share in the fiscal year.
Its shares moved as high as $100 a share in March.
Thirteen of the 18 analysts following the stock maintain either a "buy" or "strong buy" recommendation.