Mo Farah will compete in his final marathon in front of a home crowd in London on Sunday, the four-times Olympic gold medallist said on Thursday ahead of his likely retirement this year.

The 40-year-old, who withdrew from last year's event due to injury, has run the London Marathon three times with a best finish of third in 2018, the same year he won the Chicago Marathon.

About 750,000 people are expected to attend the race and Farah expects the occasion to be an emotional one.

"It will be my last marathon. It won't be my last race but in terms of marathon, the London Marathon will be my last," Farah told reporters.

"I started the mini-marathon here, so for me, it will be quite emotional. I remember (when I was) 14-years-old, I was here watching great athletes running on the Sunday and I was here taking part in the mini-marathon.

"The support, the people coming out in London, I think that will get to me but I will try not think about it and run. After the race maybe there might be a bit of tears and emotion."

(Reporting by Pearl Josephine Nazare in Bengaluru Editing by Toby Davis)