Naylor, who was placed on the injured list earlier Friday, was diagnosed with a right oblique strain and is expected to miss 3-to-6 weeks, Mandy Bell of MLB.com reports.
Naylor began experiencing tightness in his right side earlier this week, and an MRI taken Thursday revealed the strained oblique. David Fry could fill in as the Guardians' primary first baseman, with Gabriel Arias representing another option at the position.