Kyle Hutton remains a doubt for Rangers ahead of the round-of-32 second-leg tie in the Portuguese capital.
The youngster travelled with the rest of the squad on Wednesday morning but has been struggling with illness.
Midfielders Steven Naismith (hamstring) and Jamie Ness (groin) have already been ruled out of the clash, while Nikica Jelavic is ineligible.
Lee McCulloch was also on the flight to Lisbon but still faces several weeks on the sidelines after undergoing knee surgery, while Kirk Broadfoot and Andrew Little remain out.
The first leg at Ibrox finished 1-1.
Rangers (from): McGregor, Foster, Whittaker, Weir, Papac, Bougherra, Davis, Bartley, Edu, Weiss, Fleck, Diouf, Healy, Lafferty, Wylde, Hutton, Cole, Alexander.
