Betances has a partial tear of his left Achilles' tendon, Mike Mazzeo of Yahoo Sports reports.
He apparently landed awkwardly on the mound in his appearance Sunday and went through testing Tuesday. Surgery is not being recommended at this time but he is going for a second opinion, so surgery is not off the table either. Regardless, it's safe to say Betances' season is over. He had only just returned from a shoulder injury that wiped out almost his whole season. He is a free agent this offseason, so this injury couldn't have come at a worse time.