PHOENIX -- The Phillies’ pitching depth has been tested recently as some of their best and most reliable pitchers have landed on the injured list.

The group includes Zack Wheeler, Seranthony Domínguez and Corey Knebel.

The Phillies expect Wheeler to rejoin the rotation Tuesday against Miami. They hope Domínguez returns sometime during next week’s homestand at Citizens Bank Park. Knebel, however, is lost for the season.

The injuries have left the Phillies wondering whom to add to the roster when it expands from 26 to 28 players on Thursday. Teams can add two position players, or one position player and one pitcher in September. (Teams cannot have more than 14 pitchers on the roster.) The Phillies on Wednesday acquired Triple-A right-hander Vinny Nittoli from the Blue Jays for Triple-A catcher Karl Ellison. Nittoli, 31, will be added to the roster Thursday before Friday’s series opener in San Francisco.

“We were seeing if we could find a pitcher or two who we think might help us,” Phillies president of baseball operations Dave Dombrowski said. “He’s a guy who over the past couple months has really pitched well. He’s got a deceptive delivery. He’s got a fastball probably a tick below average. But his slider has improved a great deal. He’s thrown a very good breaking ball.”

Nittoli had a 3.30 ERA in 32 appearances this season with Triple-A Scranton/Wilkes-Barre and Triple-A Buffalo. The Yankees released him July 18 and the Blue Jays signed him July 24. He struck out 15 of the 37 batters he faced with Buffalo, walking only one.

The Phillies hope he can help.

The Phils on Tuesday signed right-hander Chris Devenski to a Minor League deal. He helped Houston win the 2017 World Series. He also made the AL All-Star team. But Devenski has struggled in recent years because of injuries. He could help at some point, if he pitches well with Triple-A Lehigh Valley.

Internally, the Phillies already had pitchers like Mark Appel, Kent Emanuel, Francisco Morales and Michael Plassmeyer on the 40-man roster. Emanuel and Plassmeyer figure to stay stretched out in the rotation. Appel has struggled recently. The Phillies simply thought Nittoli was the best option at this point.

Phillies interim manager Rob Thomson said they think right-hander Zach Eflin could pitch again this season as a reliever. He has not pitched since June 25 because of a chronic right knee injury. He is scheduled to throw another bullpen session this weekend in San Francisco.

Dombrowski said they have not decided which position player they will add to the roster. Darick Hall played well as the team’s DH while Bryce Harper was on the injured list. But if Thomson wants more defensive versatility, they could add Yairo Muñoz.

“It’s not necessarily the guy who’s performing the best, as it is who does he think will fit with how he wants to manage the club,” Dombrowski said.