Egypt's foreign-based players were ordered to arrive at their training camp on Tuesday in preparation for the tournament, which starts on January 14 in Gabon, but midfielder Elmohamady has been allowed to arrive late in order to play at The Hawthorns.
Stoke's request for winger Ramadan Sobhi to delay his arrival so he could play in Tuesday's home game against Watford has been turned down.
"We received requests from Stoke City and Hull City asking to delay the arrival of Ramadan Sobhi and Ahmed Elmohamady respectively to join the national team camp to start preparations for the 2017 African Nations Cup" Egypt's team director Ihab Leheta told reporters.
"We agreed with Hull City to delay the arrival of Elmohamady, but we refused Stoke City's request."
Elmohamady's Hull team-mate Dieumerci Mbokani is also available to play at West Brom before the striker heads off to join up with DR Congo.
Hull boss Mike Phelan is hoping to help cover the absence of those two key players by drafting in a defender and a striker during the January transfer window
Former Barcelona star Samuel Eto'o, currently with Turkish side Antalyaspor, is the latest player to be linked with a move to the KCOM Stadium, while FC Groningen defender Hans Hateboer and France international striker Sebastien Haller have also been reported as possible targets
Phelan has no new injury or suspension worries as his relegation-battlers bid to avoid an eighth straight league defeat on the road
Hull were denied a first win since November 6 at the KCOM on Friday night when Ross Barkley's late header earned Everton a 2-2 draw
Phelan, heartened by another gutsy display but clearly frustrated a much-needed win eluded his side, is set to stick with David Marshall after the goalkeeper's costly error against Everton
Marshall punched Kevin Mirallas' corner into his own net in first-half stoppage time to inadvertently cancel out Michael Dawson's early opener
"I stand by every player," Phelan said
"I know many footballers who have made mistakes and their careers were fantastic
"It's something to reflect on
You take your medicine when it comes, but you move on.
"We now find ourselves off the bottom of the league, which in itself is progress, so we look forward to Monday."
Source : PA