PHOENIX - Mets reliever Bobby Parnell's 30-day rehab clock will expire this week, meaning he will return to the roster. But his readiness is an open question.

Parnell has lacked velocity in his comeback from Tommy John surgery. In his last outing, rival evaluators clocked his fastball at 90 to 93 mph. During his career, Parnell's fastball has averaged 95.6 mph.

Manager Terry Collins hopes the big leagues will be an antidote. "You don't know until once he gets here," he said before Sunday's 6-3 win over the Diamondbacks. "Again, he may amp it up and pitch at 95, 96 a little bit. So he might have it still. But we won't know until he's here."

A power pitcher, Parnell has not been effective with diminished velocity. In seven Double-A rehab games, he has a 14.22 ERA.

According to Collins, Parnell will make one more minor-league appearance before rejoining the Mets.

Collins said Parnell, once the Mets' closer, will not be assigned to a specific role.

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Said Collins: "I think I'll just get him in there and let him get his feet wet again."

Meanwhile, fellow reliever Vic Black (neck, shoulder) was activated from the 15-day disabled list and assigned to Triple-A Las Vegas because of command issues during his minor-league rehab. Black has allowed six runs in eight innings since May 16.

Extra bases

The Mets could have catcher Travis d'Arnaud (bone bruise) and second baseman Dilson Herrera (fractured finger) back before the team's upcoming homestand. Both have shifted their rehab assignments to Las Vegas . . . John Mayberry Jr. missed Sunday's game with a left heel issue.