Cooper was up and down from the Minors to the big leagues from 1971-73, but he stuck with the team permanently from '74-76 before he was traded to the Brewers.
Cooper hasn't talked to Yastrzemski since the two were at a card show in New Hampshire in 2005, but he planned to check in with former teammate Jim Rice, who still keeps in close contact with the Hall of Famer.
"Tremendous competitor," Cooper said of Yastrzemski. "I liken that to a [Craig] Biggio kind of character. He played hard every day -- was very, very competitive. He'd dial up the intensity when he needed to. And a good guy -- you hate for him to be going through what he's going through."
Alyson Footer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.