With one win and one defeat, and their game against Pakistan washed out, the 1996 world champions are fighting to stay in the tournament.
Sri Lanka were bowled out by New Zealand for a paltry 136 runs and their batsmen struggled against Afghanistan after a solid start with experienced middle-order batsmen like Kusal Mendis and all-rounder Angelo Mathews short of runs.
"I'm confident the players of that quality will definitely come to the party soon. ...but yeah, we do need more from some of the batters," Lewis told reporters.
Bangladesh pulled off an upset win over South Africa in their opening game before losing to New Zealand and England.
"They (Bangladesh) have had a tough start to the World Cup in terms of the fixtures, some difficult ones, but they have obviously put in some good performances even in games they haven't won which have suggested they are going to be a tough opposition for everybody, so we know that," Lewis said.
Sri Lanka will be without fast bowler Nuwan Pradeep due to a dislocated finger.
(Reporting by Saikat Chatterjee; Editing by Ed Osmond)
