You dont say whether it is the R/H or L/H wrist. Ideally both wrists should be kept as straight as possible. Do you rest your forearm on the body of the bass ? IMO, it is better not to. A good idea would be to do some gentle stretching before you start a practice session. Check out the link below, where in post #6, I give links to technique.
New wrist problems
Also, here is a clip on gentle stretches for the wrist. Hope these help.
Hand Care for Musicians - Guitar, Piano, and Bass - w/ Todd Urban - YouTube