He has been recalled by Cricket Australia for treatment on a foot injury suffered while bowling during the County Championship loss to Sussex.
The county hope New Zealand's Mitchell Santner, who is playing in the T20 Blast, can be his overseas replacement.
Hastings, 31, has taken 16 wickets at 34.38 and scored 139 runs at 23.16 in his six Championship games this summer.
On Friday, he hit the second fastest Twenty20 half-century in Worcestershire's history off 19 balls against Birmingham Bears.
Director of cricket Steve Rhodes told BBC Hereford & Worcester: "Cricket Australia have asked for him to go back home.
"We thoroughly understand that - they want John Hastings back fit and want to monitor his rehab, so we'll take it on the chin.
"We'll certainly look at alternatives. In the past we've brought in Miguel Cummins, Kemar Roach and Shannon Gabriel but the West Indies are here this year.
"So we've just got the find the right one because we're desperate to go up."
Worcestershire are currently second in Division Two of the County Championship, 17 points clear of both Sussex and Kent, who have a game in hand.
Worcestershire will be without Australia all-rounder John Hastings for the remainder of the 2017 season.