put 〜 out to grass

チェルシーのランパード選手が，国内のカップ戦とチャンピオンズリオーグの決勝戦について意気込みを語っているのをThe Sunが取り上げています。

The Chelsea star lines up against Liverpool in the FA Cup Final this evening looking to complete the first stage of an historic double.
Lamps and his Blues team-mates hope a Wembley win will set them up nicely for their Champions League final against Bayern Munich in the Germans' backyard in two weeks' time.
And he is so excited by the prospect of bagging both trophies that it is keeping him awake at night.
He said: "I think about it every night, I really do. I’ve never been more aware about what a situation like this means.
（中略）
Lampard is sure to have a big say in the Blues' big fortnight, having returned to form under interim manager Roberto Di Matteo after previous boss Andre Villas-Boas tried unsuccessfully to put him out to grass.
http://www.thesun.co.uk/sol/homepage/sport/football/4298508/Frank-Lampard-hopes-FA-Cup-success-today-will-lead-Chelsea-to-another-triumph-in-the-Champions-League-final.html

put one out to grassは「（高齢などの理由で）〜を引退させる，解雇する」という意味です（『オーレックス英和辞典』旺文社）。この表現はもともとput the cattle out to grassのように「〜を放牧する」というところから来ています。競走馬が引退し、草をはみながら余生を送りという図も浮かんできます。関連してturn out a horse to grassという言い方もあります。（Sugiuchi）