The phrase "a possible exception is" is correct and usable in written English.
It can be used when discussing a situation where something may not apply or where there is an alternative case to consider.
Example: "Most employees are required to work on weekends; however, a possible exception is for those with prior commitments."
Alternatives: "an exception might be" or "one possible exception could be".
A possible exception is:Inventory control.
A possible exception is the recent IRONMAN study, which showed that iron supplementation resulted in an increased Hb level at hospital discharge compared to placebo [15].
(A possible exception is the Pythagorean Philolaus, who may have held that the soul is an 'attunement' of the body; cf. Barnes 1982, 488-95, and Huffman).
(A possible exception is guided imagination of the sort generated by stories and works of art; for discussion of these issues, see section 5.1 below).
Furthermore, although constituent order is a vital aspect of the realization of Mood type in English, the order of constituents is not relevant to the selection of Mood in BH, although a possible exception is discussed below in section Mood type.
A possible exception is if the employer's state recognizes same-sex marriages or civil unions.
"An early assessment suggests that the report brings few surprises, with a possible exception being the kickback against the Lloyds-HBOS merger.
Highsmith sympathizes with her murderers and psychopaths, while not approving of their actions (a possible exception was Ripley's dispensing of two Mafia louts, in "Ripley's Game". "He hates the Mafia, genuinely -- and so do I," she told an English interviewer).
A possible exception was L146A, where some inhibition appeared to remain, although inspection of Figure 1C suggests that this mutation does not completely abolish glycogen binding either.
A possible exception was C. hominis subtype family Ia, which showed an association with nausea and vomiting at first infections but did not show such an association in the cumulative analysis of all infection episodes (Table 5).
A possible exception was in older men with a trend between the NEAP and the femoral neck but not lumbar spine BMD, whereas no association was found with PRAL.
