Rapid Vienna fans are aghast as one of the teams most important players has been diagnosed as suffering from meningitis.Club bosses announced today (Thurs) that doctors were unable to attest for the moment how long Markus Heikkinen would be ruled out.The 31-year-old midfielder has been a regular instalment in coach Peter Pacults starting eleven ever since he joined the 32-time league champs from Luton Town FC in 2007.Heikkinen underwent a health check recently after having been strained by constant headaches for some time. Rapid officials said the Finnish national team ace would be hospitalised for at least a week to undergo infusion therapy.The diagnosis will force Pacult to make changes to his preferred line-up when his team clash with FC Porto in the UEFA Europa League in an away from home match tonight (kickoff: 9.05pm). Private channel Puls 4 will screen the match live before broadcasting the best scenes from Austrian Bundesliga title-holders Red Bull Salzburgs encounter with Manchester City.Rapid who lost the Vienna derby against Austria Vienna 0-1 on Sunday managed to qualify for the new competition for the second season in a row. They kicked out Premiership giants Aston Villa in the final playoff round both last and this season.Pacults squad will also face Turkeys Besiktas and Bulgarian club CSKA Sofia in the group stage of this seasons Europa League.Rapid only recently signed former PSV Eindhoven striker Jan Vennegoor of Hesselink in a bid to replace Croatian ace Nikica Jelavic, who joined Glasgow Rangers last month.Austria Vienna captain Milenko Acimovic, meanwhile, said he had decided to retire instantly due to permanent knee problems that had failed to disappear after surgery last April.The 33-year-old ex-Slovene national team midfielder was signed by the vice champions three years ago. He had previously played for Ittihad FC in Saudi Arabia and French side Lille OSC.