Tribal Football
·24 January 2022
Tribal Football
·24 January 2022
The 19-year-old has 12 caps for Estonia despite having not made his first-team debut at Arsenal.
Hein signed a long-term contract with the Gunners last year and will be looking for some first-team experience in the Championship.
Reading boss Veljko Paunovic said: "Karl is an international goalkeeper with good temperament, obvious ability and the hunger to improve and impress.
"He is a welcome addition to our squad and will increase the strength of our team for our remaining fixtures this season."