Sestina suffered the injury in Tuesday's practice.
"We finally get our entire team back yesterday," Calipari said in a video on Twitter. "We're finally a full team. We haven't been a full team in over a month. Nate goes to shoot a layup, it gets blocked, he falls back, goes to stop himself, breaks his wrist/hand. Out three to four, approximately four, weeks. And now we regroup. Next man up."
Sestina, a 6-foot-9 graduate transfer from Bucknell, has started all six of Kentucky's games this season. He's averaging 7.3 points and 7.2 rebounds but has struggled with his outside shot, going just 3-for-13 from beyond the arc. Sestina was expected to provide a different dimension to Calipari's frontcourt after averaging 15.8 points and 8.5 rebounds and shooting 38.0% from 3-point range last season at Bucknell.
Without Sestina, Calipari will likely move EJ Montgomery into the starting lineup alongside Nick Richards. Richards is having his best season in Lexington, averaging 14.0 points, 8.2 rebounds and 2.5 blocks. Former five-star recruit Montgomery, however, is still looking for his breakout performance after missing three games with a right ankle injury earlier this season. The Wildcats could also go with a smaller lineup at times, moving 6-foot-6 Kahlil Whitney or 6-foot-7 Keion Brooks to the power forward spot.
According to the school, Sestina is the eighth different Wildcat to suffer an injury this season.
No. 9 Kentucky (5-1) hosts UAB on Friday. With Sestina potentially out for the next month, there's a chance he would miss back-to-back games against No. 10 Ohio State and No. 2 Louisville in late December.