Lines was stretchered off in the defeat to Yeovil at the weekend with soft tissue damage to his shin and will be out of the match at the Memorial Stadium.
Apart from the 23-year-old, manager Paul Trollope has a fully-fit squad ahead of what he describes as their "toughest week of the season".
He told the Evening Post: "We are going into it on the back of three disappointments, but it is a time to show what we are about both physically and mentally because we know it will be a tough test against Leeds.
"It will be a big crowd, they are one of the best teams - if not the best team - in the division, so we know the challenge is there - and that will also be the case when we go to MK Dons at the end of the week.
"We need to clear our minds and show a real strong unity and mentality to be able to cope with the next two games."