PARIS: The group stage of the Europa League kicks off on Thursday, with the trialling of five on-pitch match officials providing the biggest talking point prior to the start of the tournament.

In the biggest change to the game since the introduction of the back-pass rule in 1992, two extra officials will patrol the area behind each goal on the lookout for penalty area transgressions such as diving and shirt-pulling.

UEFA president Michel Platini has pioneered the idea and says it will be escalated to next season's Champions League and the 2012 European Championship if it proves effective.

"One day players will give up simulating because referees will see them," said the former France international legend.

"For years players have cheated because the referees were not of a good enough quality.

"I am convinced, with the extra officials, that if you have referees close by it will prevent players from simulating and they will take the right decision."

The Europa League replaces the UEFA Cup as the continent's new second-tier cup competition, with an unprecedented 48 clubs set to contest the group phase. The top two teams from the 12 groups will go through to the knockout phase alongside the eight third-placed teams from the Champions League group stage.

Round-robin groups of four have replaced the UEFA Cup's five-team groups, in a bid to streamline the re-branded tournament along the lines of its hugely popular sister competition.

Valencia, Villarreal, Roma, Lazio, Everton and Hamburg are among the favourites to make the final in Hamburg on May 12.

Valencia have been drawn alongside current Serie A leaders Genoa in Group B, a pool that also contains French side Lille and Slavia Prague of the Czech Republic.

Villarreal, meanwhile, will go into their Group G opener at home to Bulgarians Levski Sofia without midfield lynchpin Marcos Senna, who picked up a thigh injury while on international duty with Spain.

"This is the worst news we could have received," said Villarreal coach Ernesto Valverde.

"It's a problem for us as we have seven games in the space of 22 days and we need all of our players 100 percent fit. Marcos is very important for us and his absence will be felt."

A knee ligament injury to Everton captain Phil Neville has given the Toffees defensive problems prior to the visit of AEK Athens in Group I.

The former England man had been pencilled in to replace suspended right-back Tony Hibbert, as new signing Jonny Heitinga is ineligible.

Claudio Ranieri takes Italian giants Roma to Switzerland's FC Basel in his first European assignment after replacing the sacked Luciano Spalletti.

The 'Giallorossi' began life under Ranieri with a 2-1 league win at Siena on Sunday and the former Chelsea coach is now looking forward to continuing his predecessor's exploits on the European stage.

"I cannot say my team will play as brilliantly as Spalletti's side, but I think I can bring pragmatism," Ranieri said.

"As an outsider I said Barcelona, Roma and Arsenal had been playing the best football in Europe in recent years. I was proud of Roma, especially for its image outside Italy where many people think that we only play Catenaccio. Spalletti did a tremendous job here."

Shakhtar Donetsk, who beat Werder Bremen 2-1 in the last ever UEFA Cup final in Istanbul in May, travel to Belgium to face Club Brugge in Group J, with Bremen visiting Portugal's Nacional in Group L.