Helan, who has missed the last two games due to a groin injury, may return to boss Stuart Gray’s starting line-up, but Joe Mattock could be out for the rest of the season.
Mattock sustained a groin injury in training on Thursday, while fellow defender Claude Dielna (hamstring) will also struggle to feature again this term.
Striker Will Keane (ankle) is not expected back and both Glenn Loovens (hamstring) and Jose Semedo (ankle) are still out.
Charlton can welcome back Chris Solly and Yoni Buyens after suspension.
Right-back Solly missed Tuesday night’s 1-1 draw with Fulham after he was sent off at Millwall on Good Friday, and midfielder Buyens has completed a two-match ban for collecting 10 yellow cards this season.
Skipper Johnnie Jackson is nearing a return following two months out with a leg injury and will be assessed.
Callum Harriott continues to be sidelined with a foot injury and Franck Moussa is out for the season due to a knee problem.