Liriano was carried off the field on a backboard. The team said he was expected to be hospitalized overnight for further testing and observation.
The pitch from Matt West of the Los Angeles Dodgers went under the brim of Liriano's batting helmet and hit him on the left side of the face in the eighth inning. Liriano went to the ground while holding his face and rolling in pain, and trainers rushed to his aid. He was carted off the field for transport to a hospital blocks away from the ballpark.
The 24-year-old from the Dominican Republic was acquired from San Diego in a trade Jan. 28. He made his major league debut in 2014 with the Padres and spent last year in the minors.
Liriano's left eye appeared to be severely swollen as he was strapped to the backboard.
"He's conscious, but ... it's serious," Brewers manager Craig Counsell said. "I don't know. He got hit in the head. I can't give you many details."
Jake Elmore was hitting two batters behind Liriano.
"We couldn't really see it from the field," Elmore said in the clubhouse. "The guys were saying that his nose was gushing blood, and it really hadn't stopped when he came in here.
"They said it just ticked the side of his helmet and got his cheek area. You know that the sound is different -- that slap against the flesh. That's when you know it's not good."
Liriano is trying to earn a roster slot, with center field the open spot right now. He played center in the game Sunday and was 0-for-3 before being hit.
Lirianobatted .292 with 14 home runs and 64 RBIs for El Paso in the Pacific Coast League last season.
"We're all praying for him," Brewers pitcher Jimmy Nelson said. "It's tough for him and his family. Hopefully, everything comes back, and he's OK, and it's not too severe. It is tough, and it kind of makes you appreciate every day."
Nelson started and gave up one run and four hits in six innings.
"Stuff like that, when it's that quick, it can be a matter of inches between something that's severe and not as severe," Nelson said.
Scott Kazmir started for the split-squad Dodgers and allowed one earned run and four hits in four innings.
Ryan Braun had an RBI single for Milwaukee. He has recorded a hit in all three games he has played in his return from offseason back surgery.
Information from The Associated Press was used in this report.