The news comes as a further setback for Keane, who has also had Mark Kennedy ruled out for three weeks.
Both players suffered hamstring injuries during the defeat against Barnsley last weekend.
Keane told the club's website: "It looks like Luke will be out for around about five weeks.
"It`s the first hamstring injury he has had, and he couldn`t gauge whether he had torn it or not, and I can understand that. Credit to the lad though, he played on, and I admire that."
Source: PA
Source: PA