Ospreys lock Evans tore a pectoral muscle playing for Swansea in the Principality Premiership match against Pontypridd after using the semi-professional fixture to boost his match fitness following a near year-long absence with knee damage.
And while Gatland has second row cover in the shape of Luke Chateris, Ian Gough and Deniol Jones, he has less options in the front row after Yapp and Jones tore a bicep and groin respectively.
Jones had been tipped to step in for Jenkins against the All Blacks on November 7 but he is not expected to return to action until the Ospreys' Magners League match against the Blues on October 24.
Ironically, Jenkins is hoping to appear in the same game.
Gatland has been boosted by the news that Williams could yet be in contention for the opening November Test against Graham Henry's men, however, after it was announced that he could recover from shoulder surgery by the end of the month.
"Martyn is ahead of schedule and he is probably about two to three weeks from playing," said Williams' head coach at the Blues, Dai Young.
"That means he could be available for the week before the New Zealand game."