Thielbar could be out "a matter of days or potentially weeks" due to a back strain, manager Rocco Baldelli told MLB.com.
Thielbar was hurt early in training camp. His status for Opening Day looks in doubt as a result. Thielbar's unique curveball (he didn't allow a hit the 94 times he threw it last season) and prowess against left-handed batters (.376 OPS allowed) had him set for a regular role in the bullpen.