Henn, who will work out of the bullpen, was available for Wednesday's game against the Red Sox.
Right-hander Koji Uehara, who was placed on the disabled list June 27 (retroactive to June 24) with elbow tendinitis, was also in the clubhouse before Wednesday's game. Unlike Henn, though, Uehara was not available for the game, and his availability remains uncertain.
"He's not ready to pitch in a game yet," said Orioles manager Dave Trembley. "That's the information that he's giving us. He [threw] a sideline today with [pitching coach] Rick Kranitz, and I just spoke to Rick and he would say that [Uehara's] going to need one or two more sidelines. I'd like to get him to possibly throw a simulated game and throw to some hitters. He relayed this information before he got here today that he doesn't feel as if he's ready to pitch in a game yet.
"So when we go to New York on [Friday], he probably will throw a sideline again or maybe throw to some hitters, because we have extra guys that we're bringing out early anyways for extra hitting. So maybe we'll do something like that."
In 12 games this season, his first pitching in Major League Baseball, Uehara, 34, posted a record of 2-4, with a 4.05 ERA. In 66 2/3 innings, before being shut down in late June, he had given up 71 hits, including seven home runs, and 12 walks while striking out 48 batters.
Before rejoining the team, Uehara had been rehabbing at the team's complex in Sarasota, Fla.
"I was told [Tuesday] that after Koji's last side session in Florida, which he threw 40 pitches, he told Dave Walker, our medical rehab coordinator, that he needed more time to throw," Trembley said. "That he was not, in his estimation -- he was not ready to pitch in a game yet. That's what Koji said."