How likely is it for a man to contract chlamydia by receiving oral sex from a woman?

Mouth to penis CPR?: It is unlikely to transmit chlamydia unless the woman's mouth is already infected. In that case, it could produce a reaction(cpr). The mouth is rife with bacteria as opposed to the "cleaner" vagina, so before one "biblically knows" a partner, it is a great idea to know your partner well and remain monogamous.

Unlikely: The sexually transmitted form of chlamydia is localized the gential and urinary tracts.

Possible: In general, not likely. However, chlamydia can be found in the oral cavity due to oral sex with someone infected with chlamydia or from other contacts. I there is then oral sex and enough innoculation, the male can get urethral infection from the saliva and oral mucosa.