The Mariners on Friday made their lineup deeper and their bench shallower.

They added Josh Naylor to the active roster and optioned Miles Matrsobuoni to Tacoma. The moves come a day after the Mariners acquired Naylor in a trade with the Diamondbacks.

The Mariners could have moved on from the severe struggles of Donovan Solano or Dylan Moore. Instead, they optioned Mastrobuoni and raised a number of questions about how the lineup will operate going forward.

Naylor is a lefty first baseman with large handedness splits (144 wRC+ vs. RHP; 88 wRC+ vs. LHP). The Mariners have used a platoon at first base all year, with Rowdy Tellez and Luke Raley against RHP and Solano against LHP. On the one hand, it’s worked, as the Mariners have a 126 wRC+ at first base against RHP. On the other, it hasn’t worked, as they have a 40 wRC+ at first against LHP — worst in MLB. These numbers also don’t include Solano’s 1-for-23 as a pinch hitter, further sinking the platoon’s overall effect.

Naylor could represent an improvement for the Mariners at first base against LHP, but it’s not clear if they plan to use him in a platoon or as the full-time first baseman. Solano’s last remaining role with the team appears to be on the short side of a first base platoon, whereas Mastrobuoni could play just about every position on the field. Mastrobuoni has struggled this year with an 86 wRC+, but he’s been a bit better by “expected” metrics on Baseball Savant. Kate Preusser recently noted for the site that Matsrobuoni has been solid off the bench, and the Mariners seemed pleased with what they’ve gotten from him this year. Solano hasn’t been better at the plate with an 82 wRC+, and he’s in the second steepest slump in MLB at the moment. Both players are projected for 0.0 fWAR the rest of the season. Perhaps the Mariners simply preferred to exercise an available option, or perhaps Solano still has a role on the team.

We could get that answer tonight tonight. Naylor will bat fourth in the lineup against a righty.

The Mariners face RHP José Soriano to begin the game, but the Angels have three LHP in the bullpen. If Naylor gets to face one late, and especially if he starts against LHP Tyler Anderson on Saturday, that bodes well for his future as the team’s true first baseman.