Irvine wanted both signings to feature after Preston had secured Championship status which they did on Saturday but they will now play because St Ledger and Jones have been ruled out for the season.
Jones suffered a gash on the back of his heal which required stitches and needs time to heel which will mean that Jones is set to miss out for the final two games of the season.
St Ledger has also suffered a hamstring injury which means that he too will miss the remainder of the season. Trotman played as a substitute on Saturday at Plymouth and is likely to start in the centre alongside Mawene with Hart to start at right back.