Tonkin has allowed seven earned runs -- including three homers -- over his last 10 appearances, spanning 14.1 innings.
The 26-year-old has been inconsistent this year, posting a 0.88 WHIP in July, but a 1.61 mark in May and 2.14 so far in August. He also hasn't gotten the opportunity to pitch in close games, earning just two holds in three chances this year.