September's World Cup may come too soon for rugby league convert Sam Burgess to make it into the England squad, says coach Stuart Lancaster.
Burgess, 26, joined Bath from Australian club South Sydney Rabbitohs and made his debut for England Saxons last month.
Club coach Mike Ford said Burgess is "frustrated" with aspects of union.
Lancaster said: "The Six Nations was always going to be a push. The World Cup would be too, but never say never."
Speaking to BBC Radio 5 live, Lancaster said he still thinks it is early days to judge the development of the former Bradford Bulls prop forward.
He said: "He wants to play rugby union, he wants to play for England and Bath at the highest level.
"I know one of his ambitions is to try and get on the Australia tour in 2016 and try and become a regular international player in 2017.
|Sam Burgess profile|
|Sam Burgess made his professional rugby league debut with Bradford Bulls in 2006, going on to score 17 tries in 88 matches for the club. Four years later, he headed to Australia to play for South Sydney Rabbitohs, playing 95 matches and scoring 26 tries. He returned to England last winter, switching codes and joining Bath.|
"So his mindset is a bit broader and mine is also. I'm happy with what he's doing 100%."
Having coached players who have made the change of codes, Lancaster says he is under no illusions as to how long it can take.
"I think the expectation around what a player can achieve - having come from one code to another - is very high, but the reality is he hasn't looked out of place at all in some of the top-end club games in rugby union.
"I know he probably feels he wants to make more of an impact but sometimes the games in rugby don't go that way."
Bath boss Ford revealed Burgess's frustration in second-placed Bath's 21-13 Premiership defeat by leaders Northampton.
He said: "It frustrates him a bit. The scrums frustrate him, the time the ball is out of play. He's standing around getting cold. He has to deal with all these things.
"The last two weeks we've had a plan to get Sam in the game from set-piece, and we've not delivered.
"He will have 20 carries in rugby league and here it is four or five."