Serbia captain Branislav Ivanovic feels Ireland are going to arguably be the toughest challenge for his country in the 2018 FIFA World Cup qualifiers.

The Boys in Green open their campaign on Monday with a trip to the Serbian capital Belgrade where both sides will hope to make a good start en route to world football's showpiece event which will be hosted in Russia in the summer of 2018.

Austria and Wales are also both in Ireland's group with those four sides expected to battle evenly for the automatic qualification and playoff spot. Moldova and Georgia are the other sides in the group and are potentially tricky opponents on their day.

Chelsea defender Ivanovic is impressed by Ireland and says that he expecting a battle on Monday if Serbia are to overcome Martin O'Neill's side.

"Ireland is a very difficult opponent to start the qualification with – I would say the most difficult, probably – but if we play like we did and like we have trained for this type of play, then we can do well," he said.

“Ireland is an opponent that needs to be respected, that demands respect, and what I am especially impressed about is their level of continuity."