Barnsley have sold Kieffer Moore to their Championship rivals Wigan Athletic for £4million.
The striker, who turns 27 on Thursday, netted 23 goals in 56 Reds games following his move from Ipswich Town in January last year - including 19 to help them gain promotion last season.
He missed Saturday’s 1-0 win over Fulham on the opening day as the deal was being completed.
The Reds’ statement claims Moore asked for the move, while co-owner Paul Conway has said all transfer fees received will be re-invested in the squad.
Barnsley are now in the hunt for another striker before the transfer window closes on Thursday.