Less than a week after the Mets got a hopeful glimpse of a future ace, they got some unsettling news about their current one. Johan Santana, who was shut down early last season, has weakness in his surgically repaired left shoulder and will have his Grapefruit League debut delayed, the Mets announced Friday.

Emphasizing that there was no injury, GM Sandy Alderson said that Santana was not ready to make his first spring start on March 2, as announced. Instead the Mets said he will debut between March 10-15.

The weakness in Santana’s shoulder was obvious when he tried to throw off a mound Wednesday. After 20 pitches in chilly weather on Sunday — the first time he had thrown off a mound since August — Santana struggled in a session in front of manager Terry Collins.

“He didn’t have the arm speed,” Collins said. “You could just tell.”

While the Mets remain optimistic that Santana will be ready to start the April 1 season opener, the delay leaves no room for further difficulties. Alderson was asked if the start was endangered.

“Right now we don’t think so,” the GM said. “Obviously it’s a possibility, but right now we’re still shooting for Opening Day.”