Spencer Howard’s rookie season could end two weeks short, as the Phillies starting rotation suffered another blow Sunday morning with the right-hander placed on the injured list with shoulder stiffness.

Howard’s injured-list stint will cost him at least two starts, but it would not be surprising if the Phillies stressed caution with their top pitching prospect instead of rushing him back to pitch one of the season’s final four games.

Phillies manager Joe Girardi said Howard felt better Sunday than he did on Saturday, when his sore shoulder forced him to leave his start after throwing 66 pitches.

“You have to find out exactly what’s there,” Girardi said. “It may just be a stiff shoulder for whatever reason, Maybe he slept on it funny. We’ll go from there.”

The Phillies are already without Zack Wheeler, who might be able to pitch this week against the Mets if his fingernail is healed after he ripped it last week while putting on jeans. He played catch on Sunday, throwing 10 fastballs off the mound at 80% effort. He is expected to complete a bullpen session on Monday.

And now they are without Howard, as they begin the final two weeks of the season. He has a 5.92 ERA in six starts since being promoted to the major leagues.

Howard will likely be replaced in the rotation by Vince Velasquez, who will pitch Monday’s series finale against Marlins right-hander Pablo Lopez. But if Wheeler’s absence is prolonged, the Phillies will be hard-pressed to find a starter to replace him.

Extra bases

The Phillies transferred Jose Alvarez (testicular contusion) to the 45-day injured list, which means his season is likely finished. ... Connor Brogdon was promoted from Allentown, pitched two scoreless innings, and sent back down.