Estrada was on the 60-day injured list due to a back strain, and after struggling through his last three rehab outings, he's been issued his release. The veteran right-hander accrued an unimpressive 6.85 ERA and 1.31 WHIP with 11 strikeouts over five starts with Oakland this season (23.2 innings), and he hasn't pitched in the big leagues since April 16.

The veteran right-hander was making a big leap in competition from the High-A level, and he ran into plenty of trouble during his relatively brief time on the mound. Estrada surrendered a solo home run to Sam Hillard and a double to Drew Weeks in terms of extra-base hits, pushing his ERA to 8.44 across 10.2 innings during his rehab assignment. It's uncertain where the Athletics go from here with Estrada, as he appears close to stretched out (59 pitches Friday), but he's also proven ineffective over his last three rehab outings.

The move up to the Aviators is somewhat surprising given how Estrada struggled against High-A hitters in his appearance for Stockton last Friday. Nevertheless, the Athletics will give the veteran right-hander a whirl against a notably higher caliber of competition. Estrada owns a 7.04 ERA, 1.30 WHIP and .273 BAA across 7.2 innings over four rehab starts thus far.

Estrada worked up to 55 pitches, 35 of which he got into the strike zone. The fact the veteran right-hander was so hittable was certainly concerning when considering the quality of competition he faced, and the outing marked the second consecutive in which he's allowed multiple earned runs. Estrada figures to continue toiling away in the lower levels of the minors for at least one more rehab appearance before any move up is considered.