Don't do it ... so says Cardinals star Matt Carpenter, who tells TMZ Sports Pujols deserves to be treated like a king in his first game back in STL.

"Like a hero coming back to town," Carpenter says.

Of course, The Machine famously put together a Hall of Fame career for the Cards from 2001 to 2011 ... but he didn't leave for the Angels on the best of terms following the '11 season.

Some have thought he might be welcomed with a bunch of boos because of that when he comes to town with the Halos this week ... but Carpenter says fans should stand up and cheer nonetheless.

"That guy had arguably one of the 10 best seasons that have ever been played in St. Louis," Matt says.

First pitch Friday is at 5:15 PM PT ... Pujols is expected to step into the batter's box in either the first or second innings.