Although both players were able to play in North End's 3-1 defeat to Crewe last week, Westley revealed that the midfield pair are struggling.
Wroe has been missing training sessions after having a scan on his knee with Westley conceding his performances have dropped as a result.
The Lilywhites boss also announced Holmes is troubled with an illness which may result in him being unable to play the full 90 minutes at Fratton Park.
Preston will continue to be without defender Scott Laird (broken leg) and Keith Keane (knee) as the pair are long-term absentees.
Westley has been impressed by Pompey, despite their off-field problems.
"They've got some tremendous players there with great backgrounds and great qualities," he told Preston's official website.
Striker Akpo Sodje will not be available after leaving with immediate effect after turning down an extension to his deal at Deepdale.