The 23-year-old Kipkirui had to be attended by Gor Mahia medics in the 27th minute of the closely fought battle after he collided with Collins Neto after a 50/50 challenge on the ball.
Despite receiving medical attention for over four minutes, the striker continued to limp and looked in pain so he was withdrawn at the start of the second half with coach Polack opting to bring in Ghanaian striker Francis Afriyie to take his place.
“[Kipkirui] has picked an ankle injury and I did not want to risk him with more playing time,” Polack told Goal after the match at Afraha Stadium.
“It is a new injury so I wanted to take a precautionary measure. You cannot take a risk with such an injury and you saw how the player was in pain.
“Our doctors will assess the injury and give us a report on Monday, but his substitution was not for tactical reasons but because he was in pain and needed to rest the leg.”
The exit of Kipkirui saw Gor Mahia struggle to break down the watertight Zoo Kericho defence and it needed the magic of Boniface Omondi to hand the champions a 1-0 result, a fourth straight win in the top-flight which moved them top of the 18-team KPL table.
Coach Polack has admitted his side struggled to contain Zoo but picked out his defence and the goalkeeper for praise.
“My defence was strong at the back and it worked to our advantage and our keeper [Mapigano] was also in good shape, they [Zoo] hit the crossbar and I think that was the only time they came close to scoring but I am very happy with the result and the performance.”
Polack has also welcomed the upcoming international break as he will use it to shape the team for the upcoming matches.
“The last game we played [against Nzoia Sugar], we displayed some good football, and this wasn’t at the same level as we have been playing before.
‘But because we have a new coach and a lot of new players in the squad we will definitely have some ups and downs and so I welcome the international break because we will work on many things to improve ahead of our next match.”
Gor Mahia will next face Kariobangi Sharks in a league match on October 20.