World Rugby is looking into the appointment of a Romanian referee for a crucial match between Spain and Belgium that determined whether Romania qualified for the 2019 Rugby World Cup.

Spain's 18-10 defeat in Brussels on Sunday meant Romania advanced to the World Cup through a second-place finish in the Rugby Europe Championship.

Spain would have qualified with a win.

Spanish players were left fuming over the performance of Romanian official Vlad Iordachescu, pursuing him after the final whistle as coaching staff tried to restrain them.

Spain's rugby federation said it had warned Rugby Europe, whose president is Romanian, about appointing a Romanian referee for a game of such importance for both nations.

The two assistant referees for the match were also Romanian.

Players of Spain including Guillaume G Rouet confront the referee after defeat in the Rugby World Cup 2019 Europe Qualifier match. (Photo / Getty Images)

The game's governing body World Rugby, which does not appoint match officials for Rugby Europe Championship qualifiers, says "it is in contact with Rugby Europe to understand the context of events relating to the Belgium v Spain match in Brussels on Sunday."

Spain coach Santiago Santos criticised Iordachescu in his post-match news conference, accusing him of not allowing his team to play.

"The difference between penalties against us and for us was huge," Santos said.

"When we were trying to come back in the game the play kept on being interrupted. I said to one of the players that Spain didn't lose today, rugby lost."