The left-hander fell to the ground after getting hit by a comebacker hit by David Fletcher.
Kikuchi was writhing in pain when catcher José Godoy tried to throw out Fletcher at first and threw into right field, allowing Taylor Ward to score from first.
Kikuchi left after receiving assistance from trainers and the Mariners' coaching staff. The Mariners said the injury was a right knee contusion.
Seattle manager Scott Servais said after the game that Kikuchi will be examined again on Sunday.
"We don't think it is a fracture. We'll wait and see how he feels and go from there,'' Servais said. "He was throwing the ball great and was on top of his game until the line drive took him out.''
Kikuchi, who came into the game with a 3-3 record, was pitching well. He had eight strikeouts and allowed two runs, both on home runs, through the first four innings.
It would be another blow for the Mariners if Kikuchi had to go on the injured list. Already this week, right-hander Justin Dunn went on because of right shoulder inflammation and shortstop Kyle Lewis, last season's American League Rookie of the Year, is expected to miss a significant amount of time because of a torn meniscus in his right knee.
The Associated Press contributed to this report.