Director of sports medicine Todd Tomczyk said that Vazquez experienced left forearm discomfort after his final two pitches in the Pirates' 6-4 loss to the St. Louis Cardinals. Vazquez was not available postgame and will be re-evaluated Monday.
"We haven't seen him in this lane before as far as being inconsistent with the command, especially the fastball,'' Pirates manager Clint Hurdle said before Vazquez was examined by the training staff. "It's been something that's really been in a good place. We'll keep hunting it and so will he.''
Vazquez came on with one out in the eighth after St. Louis loaded the bases off Pittsburgh reliever Michael Feliz (0-2).
Harrison Bader fought off a 99 mph fastball from Vazquez and dumped it into shallow right field to tie the game at 4-4. Vazquez then walked Yairo Munoz on four pitches to force in the go-ahead run, and the Cardinals added another run on a fielder's choice for the victory.
The Pirates closer, who changed his name from Felipe Rivero earlier in the year, had blown saves in his previous two outings, against the San Diego Padres last Sunday and the Cincinnati Reds on Wednesday.
The Associated Press contributed to this report.