Although a scan showed the muscle was strained not torn, Baros will only feature against Russia in Friday's Group A game if can train with the full team on Thursday, Krejci added.
"If Milan does the full training session with the team, he will be ready to play," Krejci said. " If he trains on his own, he will not."
While the 29-year-old Galatasaray striker has only scored three times in the past two years for the Czechs, coach Michal Bilek has few experienced options beyond Baros who was the Golden Boot winner at Euro 2004.
If he is not ready to lead the attack, Nuremberg's Tomas Pekhart is likely to take on the main striking role. Another option is Jablonec's David Lafata who led the Czech league in scoring last season.
However, neither has the pedigree of Baros, who has scored 41 goals for the national team. Pekhart has yet to find the net for the Czechs while Lafata has three international goals.
After facing Russia at the Municipal Stadium, the Czechs will play co-hosts Poland and former European champions Greece in the group stage of the event also being staged in Ukraine.
Meanwhile Netherlands centre back Joris Mathijsen is "80 percent out" of their Euro 2012 Group B opener against Denmark on Saturday after suffering a setback in his recovery from a hamstring injury, coach Bert van Marwijk said.
Mathijsen again trained on his own for almost the entire session on Wednesday but he could only jog gingerly and did not touch the ball.
Van Marwijk told a news conference: "I am willing to take a risk but we will see in the next two days what will happen."
Wilfred Bouma, who only made the squad at the last minute, is being tipped as a potential replacement for Mathijsen given his greater experience than the other contenders.
Mathijsen was injured during the 2010 World Cup finalists' 2-1 loss to Bulgaria in a friendly last month.