iStock

Spirit Airlines  (SAVE - Get Report)  on Monday touched a 52-week low $34.53 after Buckingham Research Group downgraded the stock to neutral from buy, saying revenue challenges are "set to worsen."

Analyst Daniel McKenzie also cut the ultra-low-cost carrier's stock to $41 from $69.

The stock finished down 2.5% at $36.14.

BRG in July 2018 upgraded the stock "on increased comfort with margin expansion," McKenzie said in a Sept. 9 note.

What's changed: "three quarters of margin expansion are now being following by margin contraction. We're trimming our 2019/2020 pre-tax outlook by 13%/26% which in turn leaves us 13%/21% below consensus this year and next respectively."

BRG also sees risk to its revised outlook on off-peak revenue weakness that could worsen later this winter such as the "ungrounding" of the Boeing 737 MAX planes and increased competition.

Revenue is also expected to be hurt by Hurricane-Dorian-related cancellations.

"We've argued shares of SAVE were dead near-term but that the underlying fundamentals were intact given SAVE's superior and sustainable cost position," the analyst wrote.

"We've fallen on our sword as the stock has since declined 33% and round-tripped our upgrade. And based on the schedules data this winter, we're concluding [the] off-peak revenue story likely worsens from here."

The stock is down about 27% over the past year and has dropped about 46% from a 52-week high of $65.35 in early December.