The postponement of last night's SPFL Premiership tie against Dundee United means that Mannus still has to serve one remaining game of the two-match suspension he was given after being sent off against Hearts earlier in the month.
Last night's Tayside derby was called off in the afternoon after a pitch inspection found the surface to be too waterlogged. Hearts' Ryan Stevenson, who was also sent off during the same incident, will be clear to play in the other semi-final - against Inverness Caledonian Thistle - after the Tynecastle club rearranged their match with St Mirren for Wednesday evening.
"It is a hammer blow for me," said Mannus. "I wasn't counting any chickens but I had been looking forward to the semi-final. But the club is bigger than any one player."