FC Basel knocked United out of the Champions League this season, but the Swiss side risk being kicked out of the competition.
The Swiss Football Association will be forced to punish FC Sion for fielding ineligible players in their match against Celtic before 13 January, or Fifa will suspend Switzerland and their club sides.
“As a consequence, all matches in which the relevant players participated shall be declared forfeit or three points shall be deducted respectively,” Fifa said.
“Should this deadline not be respected, the Swiss FA will be automatically suspended from 14 January 2012 onwards.”