Chapman nearly ready

Manager Bob Melvin provided encouraging news on rookie third baseman Matt Chapman, who made a bang in his major-league debut series against the Yankees over the weekend. The knee infection that forced him to miss the first three games of the Astros series is responding to medication.

The swelling is down and Melvin expects Chapman to return Thursday or Friday, when the A’s open a three-game series in Chicago against the White Sox.

Chapman went 3-for-14 against the Yankees. His first big-league hit was a two-run single in the eighth inning Friday night that gave the A’s a 7-6 victory.

Now that Chapman got a small taste of the big leagues, the 2014 first-round draft pick is aching to return to the field.

“I have talked to him. He wants to play,” Melvin said. “He’s not happy about this. If it were up to him, he’d be out there tonight, but that’s not prudent. He had the biggest four days of his life in the Yankees series. He wants more of that.

“To be on the shelf because of an injury that’s not really baseball-related — it is baseballrelated, but it’s a freak injury — is not making him happy.”

The A’s believe the infection stems from a collision with a wall in the minors before his call-up that cut his leg and caused it to bleed. Semien rehab: Shortstop Marcus Semien will start another “spring training” when he begins a rehab assignment with Class A Stockton on Friday night, just over two months since undergoing right-wrist surgery.

Melvin cautioned this will not be a short rehab. Semien will alternate between shortstop and designated hitter while getting three at-bats a game to start, just as a player would in March.

“We’ll monitor him,” Melvin said. “I don’t want to put a number on it, but it’s not going to be one, two, three or four days.” Briefly: Chris Bassitt (Tommy John surgery) threw another side session in which he stopped, then restarted to simulate pitching multiple innings. There is no timetable for his next step, throwing to hitters. … Reliever Ryan Dull (right-knee strain) is expected to throw a bullpen session next week.