2:21 PM PT -- TMZ Sports has obtained the police report from McGuire's arrest ... and cops say a witness told them the Blue Jays catcher had been masturbating in his parked car before they arrived on the scene.
According to the report ... cops say after they rolled up to the parking lot, they saw McGuire with his shirt "barely covering his genitals" and his sweatpants around his ankles.
They claim in the report when they got McGuire out of his car, he "had an erection which was very apparent."
Cops say McGuire apologized to them profusely for the incident ... saying, "I'm sorry, I'm so sorry, this is really embarrassing." Cops say McGuire added, "I really shouldn't have been doing that."
In the report, cops claim when they got McGuire's phone to try to find his current address ... they noticed an "extremely pornographic video was playing on the screen."
Officers say they asked Reese why he came to the parking lot instead of just going home ... McGuire responded that he "did not know, it just seemed like a good place."
Toronto Blue Jays catcher Reese McGuire -- a former MLB first-round pick -- was arrested last week after cops say he was caught exposing his penis in a Florida parking lot.
The Pinellas County Sheriff's Office tells TMZ Sports ... deputies were called to a public parking lot in Dunedin, Fla. on Friday after a man was seen inside of an SUV exposing himself.
FYI, Dunedin is the spring training home of the Toronto Blue Jays -- and pitchers and catchers were expected to report to camp today.
Cops say when they arrived ... they identified McGuire as the suspect, and say he was "cooperative and did not deny the allegations."
Police say they arrested the 24-year-old ... and booked him for misdemeanor "exposure of sexual organs."
Cops say McGuire is due in Florida court in mid-March -- a spring training off day for the Blue Jays -- to face charges.
For their part, Toronto says it's aware of the allegations against its catcher ... writing in a statement, "[McGuire] has been in communication with the club and we are working to gather more information."
"Out of respect for the legal process, neither he nor the club will comment any further at this time."
McGuire has played 44 games for the Blue Jays since 2018 ... batting .297 with seven home runs.
He was selected with the 14th overall pick by the Pittsburgh Pirates in the 2013 MLB Draft ... and was later traded to the Jays in a deal that included Francisco Liriano in August 2016.