The 49ers released the following statement, which was obtained from Matt Maiocco of NBC Sports Bay Area via his Instagram page.
"The Joe Montana statue that is part of the 'The Catch' art installation located inside the stadium's Gate A plaza was vandalized following our recent Monday Night Football game. Security personnel apprehended the individual soon thereafter and the Santa Clara Police Department arrested the individual on felony vandalism charges. Crews have already begun repairs on the statue and expect work to be complete prior to Sunday's home game. As this is an ongoing police matter, we will not have any additional comment."
Maiocco reports that there was damage to the facemask of the statue, but that it has already been repaired.
Here is how the statue looked after the vandalism and before the repair.