MLB's Mark Grudzielanek Under Police Investigation Over Alleged Child Abuse

Mark Grudzielanek -- a former MLB All-Star and Gold Glove winner -- has been accused of child abuse ... and he's now under police investigation, TMZ Sports has confirmed.

Police documents show Grudzielanek is alleged to have committed the crime at around 10:30 PM on March 16 in Scottsdale, Ariz.

In the docs, Grudzielanek -- a 50-year-old who played in the MLB from 1995 to 2010 -- is listed as an "offender" ... and the alleged victim is described as a 12-year-old boy.

Details of the alleged incident are unclear ... but a source close to the case tells us the allegations stem from a physical altercation.

We've reached out to Grudzielanek for comment, but so far, no word back yet.

Grudzielanek broke into the Big Leagues in 1995 with the Expos ... and he was named an All-Star the following year.