Buck's wife's due date is tomorrow, according ESPN New York's Adam Rubin.
D’Arnaud told MetsBlog's Michael Baron that his rehab assignment will soon move to Double-A Binghamton, while he works his way back from a broken bone in his foot.
Update - 5:02 p.m.: Travis d'Arnaud is with the Binghamton Mets in Altoona, Pa. for their series against the Curve, affiliate of the Pittsburgh Pirates.
Terry Collins told reporters that it's also possible that Triple-A catchers Juan Centeno and Francisco Pena are considered to replace Buck for the few days he is out.
D'Arnaud is currently on the team's 40-man roster, while Centeno and Pena are not.
D'Arnaud was recently named the No. 23 prospect in the minor leagues by MLB.com.