MLB Star Chris Perez -- I'm Sorry for Cussing Out Fan

Cleveland Indians pitcher Chris Perez sincerely regrets verbally blasting an Oakland A's fan before the game yesterday ... this according to a team rep who tells us the GM has already spoken with Chris about the incident.

In case you missed it ... Perez -- a 2-time MLB All-Star -- snapped on an A's fan who had been taunting him about being a crappy relief pitcher. Among Perez's comebacks -- "you piece of sh*t ... get your d*ck out of your mouth."

Now, a rep for the Indians tells us the General Manager, Chris Antonetti, has already spoken with Chris and discussed the situation in full.

After the conversation, the team believes "Chris certainly regrets what he did."

We also spoke with a rep for Major League Baseball who told us the office is aware of the video and insists the incident is "currently under review."

MLB adds, "When unfortunate situations arise, we always investigate the circumstances to the best of our abilities and evaluate whether disciplinary measures are appropriate."