CHICAGO — Billy Butler missed the last two games against the White Sox because he was injured in an altercation with teammate Danny Valencia, The Chronicle has learned.

No one in the Oakland clubhouse would discuss the matter on the record, but no one denied that it occurred, either.

“No comment,” Valencia said Sunday after the team’s 4-2 loss to the White Sox. “What happens in the clubhouse stays in the clubhouse.”

Manager Bob Melvin would not comment on the incident, which occurred Friday night, according to sources. Melvin said Saturday only that Butler was out with nausea and vomiting, but he specifically ruled out the flu when asked if that was Butler’s ailment.

I feel the same, Danny has been one of my favorite teammates as well. Solid guy and a hard worker. https://t.co/Bt7f3GAlCY — Covelli Crisp (@Coco_Crisp) August 22, 2016

Nausea and vomiting typically are among the symptoms of concussions.

According to two sources, the dispute in the clubhouse began when Butler informed an equipment representative that Valencia had not, in fact, been wearing the spikes that Valencia had told the representative that he was using.

@Coco_Crisp @TheRealHos35 couldn't agree with you guys more! From college to the bigs.... A true professional ! #iGoToWarWithThatGuy! — Yonder Alonso (@YonderalonsoU) August 22, 2016

Butler, who was not available in the clubhouse after Sunday's game, did not respond to a text from The Chronicle, and A's general manager David Forst did not reply to a text and an email.

A’s players Coco Crisp and Yonder Alonso, along with Kansas City’s Eric Hosmer, tweeted their support for Valencia.

Valencia did not play in the finale in Chicago, quite possibly because of the altercation, though he also was 2-for-20 lifetime against White Sox starter Jose Quintana.

Butler and Valencia were teammates with Kansas City in 2014 as well as the second half of last year and this year in Oakland, and they are known to engage in a great deal of loud banter in the clubhouse and on the field.

Doolittle to stay on shelf: Sean Doolittle’s rehab assignment will be extended, Melvin said. The A’s had hoped to get the left-hander back this week, but Melvin said Doolittle didn’t feel quite where he wants to be yet after his outing with Triple-A Nashville on Saturday.

“He just doesn’t feel like it’s coming out of his hand the way he would like, and we’re not in a rush with him, either,” Melvin said. “He’s got a pretty good idea of when he feels he can contribute, and right now he doesn’t feel that way. I appreciate his honesty.”

Doolittle has been on the disabled list since June 26 with a left shoulder strain.

Briefly: Ryon Healy has an eight-game hitting streak, during which he is batting .355 with two homers. ... Marcus Semien, who had two doubles Sunday, hit third in the order for the first time this season.

Susan Slusser is a San Francisco Chronicle staff writer.

On deck

Monday

vs. Indians

7:05 p.m. CSNCA

Carrasco (8-6) vs. Triggs (0-1)

Tuesday

vs. Indians

7:05 p.m. CSNCA

Salazar (11-4) vs. Manaea (4-8)

Wednesday

vs. Indians

12:35 p.m. MLB Net

Bauer (9-5) vs. Graveman (9-8)

Leading off

Progress: Henderson Alvarez, yet to pitch for Oakland this season as he recovers from shoulder surgery, threw a 25-pitch bullpen session Saturday, all fastballs and changeups, and he could be on a rehab assignment soon.

— Susan Slusser