HOUSTON — Trading reliever Aroldis Chapman wasn’t necessarily a sign the Yankees are ready to dismantle because they still have a strong bullpen, but when manager Joe Girardi was asked about the effect it would have to trade designated hitter Carlos Beltran, who is headed for free agency, he made it clear that would be a heavy blow.

“Take the biggest bat out of any lineup, and how well are you going to survive?” Girardi said. “It’s not easy. With some of the other struggles we’ve had, it would become really difficult. That’s part of the reason I’m DHing him is trying to keep him in the lineup as much as I can.”

Beltran went into Tuesday night’s game against the Astros at Minute Maid Park with 21 home runs, 62 RBI and a .308 average. The manager attributed Beltran’s improved numbers this season to good health.

Girardi said the Yankees are riding Beltran, not showcasing him for trade suitors. “This is his 12th day [playing] in a row, 39 years old, that’s pretty impressive. He hasn’t had a day off since the All-Star break.”

Rodriguez still not in starting lineup

Alex Rodriguez was not in the starting lineup for the fourth straight game, and Girardi admitted A-Rod hasn’t taken ground balls at first base lately. Asked if that experiment is over, he said, “Not necessarily. It could pop up. We’ll have him take some ground balls. I think it’s important we give him a little more work before we go to a National League city.” That will come Monday at Citi Field.

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Extra bases

Rob Refsnyder played leftfield for the first time in Monday’s game and made a nice diving catch. “I think he has the ability to make plays all over the diamond because he’s athletic,” Girardi said. “I think he’s getting comfortable with the niche we’re trying to carve for him, and we expanded it by throwing him into left.” . . . Reliever Bryan Mitchell, who was lost before the season opened because of a tear in his left great toe, could return this season. “We’re not going to rush it,” Girardi said, “but his rehab has gone as well as could be expected.”