Football and week-end are, indeed, borrowed from English. For the spelling of week-end with or without a hyphen, both were in use in English, as well as a version in two words (as is often the case with newer compounds). When French borrowed it at the beginning of the 20th century, the hyphenated version was still dominant in English, so it's no surprise French would have borrowed the word with that particular spelling 
The unhyphenated "weekend" is hardly unknown in casual French usage however, in no small part because of the influence of contemporary English.
As for the meaning, a 5-day work week with days reserved for leisure and recreation is a modern invention. There was no more an established word for it in English as there was in French, and like all new technologies and cultural phenomenon, the word of the innovator or of those who helped its spread was borrowed alongside the concept itself. Weekend is in that respect similar to tea, wine, umami, opera or orange, a modern wanderwort.
In premodern societies, the division of time between rest and labour was mostly dictated by religious calendars and the need to participate in ritual, or the necessities of weather, climate and the inclination of the planet at a given latitude (and thus daylight).
Industrialisation and its increase in productivity was achieved in part through the elimination of rest through contract law, secularisation and electrical lighting. This in turn led to revendications by workers for a span of time set aside for rest by extending the Sunday break, and once achieved, the invention of new forms of recreation to fill that time of rest. A weekend is something very new.
Modern uses of the term "week-end" date to the 1870's in English. The TLFi dates the first use of the term in French to 1926. A six-day workweek remained the norm in industrialised societies until the 1930's where the 40h workweek starts to spread, sometimes only for some industries or trade, sometimes for all workers. In France, it was decided by the Popular Front government under Léon Blum in 1936 and was progressively applied to different trades. In Belgium, it was only put into law in 1964 (5x9 hours!).
I hope this demonstrates how recent the very idea of a weekend is, and how much more recent the reality of it can be. In this context, that we use a loanword for it is no surprise: it's not much older than the internet or inline skates, and contemporary with nightclubs and briefs, to cite some other concepts with names borrowed from English in French (internet, des rollers, les dancings and les slips) and much younger than football is.