The first diagnosis was a strained left adductor.
It was the final blow of a long, six-game road trip for the Suns, who finished the trip at 2-4 after losing 126-113 to the Toronto Raptors.
"I don't know how serious, or when we'll be able to evaluate," Suns interim coach Jay Triano said.
Booker, who scored a season-best 46 points Monday in the victory over the Philadelphia 76ers, had 19 points, eight rebounds and five rebounds against the Raptors.
"I hope it's nothing serious," Suns reserve forward Jared Dudley said. "Good thing we have a day off tomorrow. I hope it's just a cramp and he'll be OK. I haven't been back there yet (in the trainers' room), but I think he'll be fine."
"He's obviously one of the great young players in this league," center Greg Monroe said. "He's had an outstanding year, so you definitely don't want to see him get injured and you don't want to see anybody get injured at any point."
Kyle Lowry scored 20 points and added 10 assists and six rebounds for the Raptors (15-7) who have won four games in a row.
The Raptors entered the fourth quarter leading by 18 points.
The margin reached 19 before a Suns surge cut the lead to 10 on a 3-pointer by Dudley with 8:44 to play.
Lowry pushed Toronto's lead to 14 when he made a 3-pointer with 5:18 left.
"I thought we fought well, I just don't think we stayed mentally locked in," Triano said.
DeMar DeRozan finished with 20 points, eight assists and seven rebounds for Toronto. Serge Ibaka chipped in with 19 points, OG Anunoby had 16, C.J. Miles added 15, and Jakob Poeltl and Fred VanVleet each had 13.
"We tried to mix it up," Raptors coach Dwane Casey said. "We tried to mix up the blitzes, we tried to mix up the switches, matchups. You don't stop a young man like (Booker). I thought we just made him work for what he got ... He ended up with 19 which is a far cry from what he had (Monday) night. I'll take that, I commend our guys, we did a good job we messed up on some rotation after our blitzes. He didn't score but he did a good job of finding people behind, we did not do a good job of finding the roller. That's something we have to improve on."
Alex Len added 14 points and seven rebounds, and Troy Daniels and Josh Jackson each contributed 13 points for the Suns (9-17). Monroe scored 11 points and grabbed 10 rebounds, and Dudley scored 12.
Suns forward TJ Warren was assessed two technical fouls with 7:58 to play in the third quarter to earn an ejection from the game. He had 11 points and one rebound in 23 minutes.
The Suns picked up four technical fouls in the game overall.
"I thought we just lost our composure," Dudley said. "Frustration can set in, especially some of our young players, they haven't earned the right, you know. Obviously, you aren't going to get the calls. We're a young team that's not a winning team so we're going to have to fight the uphill battles and sometimes that happens. ... Hopefully, it was a learning experience. Last year, we had a lot of technicals."
The Raptors led by as many as 17 points before finishing the first quarter with a 36-23 lead with Lowry scoring 13. The Suns had seven turnovers in the quarter and the Raptors had none.
The Raptors led 55-46 at halftime. The Suns had a 23-19 advantage in the quarter, ending a string of 12 straight games in which the Raptors had outscored the opposition in the second quarter. Toronto made seven turnovers in the quarter and Phoenix had three.
Toronto had 18 turnovers for the game and Phoenix had 17.
Two free throws by DeRozan had the lead at 17 with 4:23 left in the third. The Raptors led 97-79 after the third quarter.
The Raptors had 30 assists.
"I think it makes it a lot easier, which makes it a lot more fun," DeRozan said. "Everybody gets a chance to touch the ball, you don't necessarily have to work so hard and it's fun. ... With that, we still missed a lot of shots but it's something we're still learning, we're still trying to get better at every time we practice, every time we play and look at film to understand what we did wrong and what we could do better."
NOTES: Suns C Tyson Chandler (rest) did not play Tuesday after recording seven points and 12 rebounds in a season-high 37 minutes Monday during a victory over the Philadelphia 76ers. Greg Monroe started at center Tuesday and Alex Len was backup. ... Suns interim coach Jay Triano became the first Canadian to be an NBA coach when he led the Raptors from 2008-2011. ... The Raptors will start a four-game trip Friday against the Memphis Grizzlies. ... The Suns will host the Washington Wizards on Thursday.