The Red Sox released relief pitcher Tyler Thornburg on Wednesday after he declined a Minor League assignment, ending the right-hander’s disappointing three-year tenure with the club.

Thornburg had been on the 10-day injured list with a right hip impingement since May 23. He was sent to Triple-A Pawtucket on a Minor League rehab assignment on June 9 and had pitched 11 times there, allowing 15 earned runs over 10 2/3 innings, although four of his past five outings were scoreless. The Red Sox faced a deadline Wednesday to activate or release Thornburg.

Hopes were high for Thornburg when the Red Sox acquired him from the Brewers in December 2016 for four players, including infielder Travis Shaw and shortstop prospect Mauricio Dubon. In 67 games for Milwaukee in ‘16, Thornburg had produced a 2.15 ERA and 90 strikeouts in 67 innings.

But things never clicked in Boston. Thornburg didn't pitch in 2017 due to a right shoulder injury, eventually undergoing surgery to address thoracic outlet syndrome. He didn’t make his Sox debut until July 6, 2018, but he struggled to a 5.63 ERA out of the club’s bullpen and didn’t factor into its postseason run.

The situation did not improve this year for the 30-year-old, as he produced a 7.71 ERA in 16 appearances for a Boston bullpen that has been in need of reliable arms. Thornburg struggled with his control while allowing multiple runs six times.

“The most frustrating thing for him is that the stuff is there,” Boston manager Alex Cora said when Thornburg was placed on the IL in May. “You see it -- 94, 95 mph. He hasn’t been able to locate his fastball when he’s ahead in counts. He hasn’t been able to put people away. The breaking ball has been inconsistent.”