He/She can also be very competitive, so I’m sure he’ll/she’ll study a lot for next time.
He/She is also surprisingly very competitive, so I’m sure he’ll/she’ll do a lot of preparation for next time.
「あの人も意外と負けん気強いところあるから、次回に向けて相当勉強してくると思うよ」は英語で He/She can also be very competitive, so I’m sure he’ll/she’ll study a lot for next time もしくは He/She is also surprisingly very competitive, so I’m sure he’ll/she’ll do a lot of preparation for next time になると思います。
あの人 – That person、He、She
意外と – surprisingly
負けん気強い – (very) competitive
次回に向けて – For next time
相当- a lot、considerably
勉強する- study
preparation - 準備、予習
イギリス 
