Mets Catcher Tomas Nido Tattoos Pet Dog On Leg, I Love My Louie!

Dog lovers will appreciate this ... New York Mets catcher Tomas Nido just showed major love to his adorable pup -- by getting a tattoo of the canine on his leg!

TMZ Sports has learned the baseball player wanted to get some ink to celebrate his beloved pet last week ... so he hit up artist Keith Hernandez from Bang Bang Tattoo in New York City.

We're told the 27-year-old handed over a portrait of his Yorkie, Louie, that he got 8 years ago ... and Hernandez then went to work.

The artist took a few hours to do the piece ... and it all ended up coming out pretty incredible!!

Check out the details ... the drawing of Louie -- which will now sit on the inside of Nido's shin forever -- looks SUPER real, right down to the fluffy hair and little dog outfit.

We're told Nido got one more tat while he was in the shop ... getting the letter "E" inked behind his ear -- a shoutout to his 8-month-old daughter, Eleni.

In total, Nido ended up sitting in the chair for about 3 or 4 hours ... and we're told he's planning to head back to the shop in the near future to get more ink done.