SEATTLE – The reports continue to be positive on Luis Severino's progress, and the Yankees are preparing to start the clock on his Minor League rehab assignment.

Having completed his second simulated game on Tuesday at the Yanks' complex in Tampa, Fla., Severino is scheduled to make his first start on Sunday for Double-A Trenton. Yankees manager Aaron Boone said that he believes the right-hander will be able to contribute in September and beyond.

"We feel like he’s throwing the ball really well," Boone said of Severino, who has missed the entire season to date with right shoulder and right lat injuries. "I'm looking forward to having him. I know what he can mean to us. There is not necessarily that rush to get him here now. I want him to be in as good a place as possible when we’re ready to take him."

The 25-year-old threw 35 pitches to Minor Leaguers on Tuesday. Assuming continued health, it is possible that the Yankees could build Severino's stamina to have him start or use him as a reliever, perhaps piggybacking with an opener like Chad Green.

"I picture him very much being part of things moving forward," Boone said. "I'll also tread carefully there. We’ve done well over the last month with him. I absolutely feel like he’s going to be a part of things. The next step is the focus right now."

In addition to Severino, right-handed reliever Trevor Rosenthal threw 25 pitches in a simulated game at the Yanks' complex. The 29-year-old Rosenthal was signed to a Minor League contract last week. He made 22 appearances this season for the Nationals and Tigers, posting a 13.50 ERA.

Questions answered

Boone said that the Yankees heard from the league office regarding Cory Gearrin's pitching motion, and they have been assured that it will not be an issue going forward. Play was halted on Monday after the umpiring crew warned the right-handed reliever that they believed he was illegally delivering a pitch due to a toe-tap, and Gearrin indeed was called for a balk during his appearance.

"My understanding is there are about a half a dozen guys in the league that have some kind of unique tap, so [umpires] have been on the lookout for certain things," Boone said. "Obviously, it's been something of a gray situation. Cory dealt with this already in May. We felt like what he is doing should be acceptable."

The league office also communicated that time should not have been called in the ninth inning of Saturday's 2-1 loss to the Dodgers, when Gleyber Torres was sent back to third base instead of being allowed to score the tying run. Boone does not seem irked by the ruling, and said that he has moved on.

"My take at the time was I didn't feel it should have been called, obviously," Boone said. "But … I think [home-plate umpire Gabe Morales] saw [pitcher Kenley Jansen] calling time. It appeared dead to him, so time was called. Hopefully it was something that we could all take and learn from."

Trainers' office

Didi Gregorius is continuing to receive treatment after being hit in the back of the right shoulder by a Clayton Kershaw fastball on Sunday. Boone said that Gregorius remains day to day and could play in Wednesday's series finale.

Cameron Maybin was out of the Yankees' lineup for a fourth consecutive game on Tuesday due to left wrist soreness. Boone said that he viewed Maybin as "a more active player" on Tuesday than he had been in the last two games of the Dodgers series and in Monday's series opener.

Comeback trail

• Dellin Betances (right lat strain) continues to work out at the Yankees' complex in Tampa, Fla. He is set to face hitters on Wednesday after completing a 20-pitch batting practice session over the weekend.

• Edwin Encarnacion (right wrist fracture) hit in the batting cage and performed fielding and throwing drills on Tuesday in New York. Boone said that Encarnacion will see live pitching in the near future.

• Aaron Hicks (right flexor strain) is expected to be re-examined on Friday with the hope of resuming a throwing program.

• Jordan Montgomery (recovery from Tommy John surgery) is scheduled to make his second Minor League rehab start later this week, potentially with Double-A Trenton. Montgomery hurled two scoreless innings on Sunday for Class A Advanced Tampa.

• Giancarlo Stanton (right PCL strain) was scheduled to take on-field batting practice with the Yankees on Tuesday.

• Luke Voit (sports hernia) is continuing his Minor League rehab assignment with Triple-A Scranton/Wilkes-Barre and remains on track to be activated on Friday for the Yanks' series opener against the Athletics. Voit is slated to play on Tuesday and Wednesday, then will be off on Thursday.

Moose call

The Yankees have announced that they will hold a celebration of Mike Mussina's Hall of Fame induction on Sunday prior to the scheduled game against the Athletics. Those attending are encouraged to arrive early and be in their seats by 12:30 p.m. ET to enjoy a ceremony featuring Mussina, his family and his Hall of Fame plaque. Mussina will also throw out the game’s ceremonial first pitch to his son Peyton.

Fans will be able to view and take photos of Mussina’s Hall of Fame plaque, which will be on display inside Gate 2 from the first pitch through the start of the seventh inning. Additionally, the first 18,000 guests will receive a Mussina T-shirt courtesy of Goldenberg’s Peanut Chews. All gates will open to ticket-holding fans at 11 a.m.

This date in Yankees history

Aug. 27, 1938: The Yankees played their fourth doubleheader in as many days, sweeping the Indians by scores of 8-7 and 13-0. Joe DiMaggio hit three triples in the first game, while Monte Pearson pitched a no-hitter in the second game.