Cubs slugger Kris Bryant left Sunday's game against Cincinnati after colliding with center fielder Jason Heyward in the sixth inning.
Speaking right after Chicago's 10-2 loss, manager Joe Maddon said he hadn't watched the replay but was told Bryant was hit in the head/neck area.
"He's doing OK. He's still under evaluation," Maddon said. "We don't know exactly what we're doing with this whole thing yet. But we're trying to talk with the docs and find out exactly where we're at."
Bryant was cleared to travel with the team to Houston for the start of its six-game road trip. He walked through the Cubs' clubhouse after the loss to the Reds, but the media wasn't allowed to speak with him because he was still being evaluated.
Bryant is batting .345 (30-for-87) with nine homers and 21 RBI in May.
Pirates general manager Neal Huntington wants Major League Baseball to consider changing its concussion assessment system to allow for player re-entry after exiting a game for concussion testing.
Huntington offered the suggestion Sunday, a day after Pittsburgh catcher Francisco Cervelli suffered a head injury.
Cervelli was struck by the barrel of Joc Pederson's broken bat with two outs in the fourth inning. After being assessed on the field by a trainer, he remained in the game before removing himself in the bottom of the inning after briefly stepping into the batter's box.
Huntington says that if a player knows he must leave a game to enter concussion testing, he's less likely to report symptoms.
In other Pirates news, top pitching prospect Mitch Keller will make his major league debut in a doubleheader Monday against the Reds.
The 23-year-old Keller is being called upon to help a depleted rotation that has struggled without injured Jameson Taillon and Trevor Williams. He'll start the nightcap after Nick Kingham pitches the opener.
Left-hander James Paxton and shortstop Didi Gregorius are closing in on their returns to the New York Yankees while right-hander Jake Barrett is heading to the injured list.
The 30-year-old Paxton has had discomfort in his left knee but is on track to rejoin the rotation this week, manager Aaron Boone said.
Gregorius homered Sunday as the DH for Class A Tampa in his second minor league rehab game. He played seven innings at shortstop Saturday. He's expected to take Monday off and then move to Triple-A Scranton/Wilkes-Barre to continue his rehab.
Gregorius, coming back from Tommy John surgery last Oct. 17, could spend a week or two with Scranton/Wilkes-Barre before returning to New York.