Leaf spot?

Hi, new to the forum but hoping someone can help. I recently had my lawn treated with a weed and feed from a local garden maintenance man. All went well for first week, all weeds went but now I have a patch of grass which is circa 8msq and pretty much square going yellow and now starting to show brown spots on the leaves. Is this leaf spot and if so could someone advise of the best way to remedy the situation please? The guy is on holiday at the moment so can't touch base with him about the issue. Thanks in advance for any help.