The Orioles selected Vazquez's contract from Triple-A Norfolk on Wednesday.
The Orioles placed O'Neill on the 10-day injured list Wednesday, retroactive to Sunday, due to right shoulder inflammation.
O'Neill relayed Wednesday that he expects to be placed on the 10-day injured list due to a right rotator cuff strain, Andy Kostka of TheBanner.com reports.
Buxton (hip) is out of the lineup for Wednesday's game against the Athletics.
Mayo is not in the lineup for Wednesday's tilt in St. Louis.
Bradley (9-6) took the loss against the A's on Tuesday after allowing four runs on seven hits and a walk while striking out 11 over 6.2 innings.
Encarnacion-Strand went 2-for-5 with a home run, three RBI and two runs scored in Tuesday's 13-1 win over the Cardinals.
Alonso went 4-for-4 with a home run, a double, four RBI and two runs scored in Tuesday's 13-1 win over the Cardinals.
Buxton was removed from Tuesday's game against the Athletics with an apparent injury, Audra Martin of Twins.tv reports.
Bassitt (5-4) earned the win Tuesday against the Cardinals, allowing one run on six hits while striking out five over 6.2 innings.
