Farbrace suggested Buttler will be retained in the XI, but faces stiff competition from fellow wicketkeeper-batsman Ben Foakes.
Buttler is averaging under 32 after 41 Tests. Foakes has only played five Tests, but has an average of over 40.
“I am worried about Jos. I think Jos should be England's wicketkeeper and batter, but he knows he can't keep going long periods of time without making contributions,” said Farbrace.
“What should a player of his ability be averaging after 40 games? It should be 40-plus. It is a lot lower than he would want it to be. I would definitely keep him for the Sri Lanka series but he needs to score runs. If not, then he has to step aside.”
Buttler in the IPL
The hard-hitting Buttler will play alongside England team-mates Ben Stokes, Tom Curran and others at the Rajasthan Royals in the Indian Premier League later this year. The Royals are priced at 10.00 by bet365 to win the 2020 IPL. Good performances during the 2018 IPL effectively reignited Buttler's Test career.
“I was watching the IPL on television a couple of years ago. Jos' shoulders were hunched. So I phoned him and asked ‘are you enjoying it?' He said ‘not really.' So I said, ‘what would your mum – who coached him when he was a boy – have said?' And he said ‘try to enjoy it.' I said, ‘well, there you are then.' He went on to make 50s in his next five games,” added Farbrace.
“We always told him not to worry about the level of expectation. Just go in and play the game and remember why you play – because you enjoy it.
“Jos is a very selfless cricketer. Everything about him as a character and person, you can see why everybody wants him in the team. He has that great knack of saying the right thing at the right time, he is a brilliant professional, he has got a lot of experience and is a team-orientated person like Stokes, Joe Root and Moeen Ali. You want those people in your team.”