The midfielder will be in Chris Coleman's Wales squad for the World Cup qualifiers with Scotland and Croatia when it is unveiled on Wednesday.
However, the Liverpool man is facing an extended period on the sidelines at some point after discovering a recurrence of an old shoulder injury had deteriorated to the point where further surgery is required.
Speaking on a tour of the Ellesmere Port car plant of Wales team sponsors Vauxhall, Allen said: "It is something that needs sorting out.
"I had an operation a few years ago and unfortunately it is a recurrence.
"It has slowly deteriorated to the point where an operation is the only thing that can solve it."
Liverpool will decide when Allen has surgery, which the 22-year-old estimates will keep him out for three months.
"I can play on, but it is all about the timing because I will be out for three months," he said.
"Obviously, I don't want to miss the start of next season if I can but we will see what the club have planned because it is a reasonably long lay-off."
With the Reds back in the running for a European place following Sunday's victory over Tottenham, Brendan Rodgers might be loath to lose Allen at this stage.
Equally, the former Swansea man would benefit from a full pre-season at Anfield, given he did not join the Merseyside giants until after his Olympic commitments with Team GB.
And next week he will be fully focused on Wales anyway, as they look to build on an encouraging win over Austria last month by completing a World Cup double over Scotland on Friday.
That initial victory over the Scots in October effectively signalled the end of Craig Levein's reign.
It also marked the climax of a tortuous period for new Wales boss Chris Coleman, who had struggled to maintain the improvements made under Gary Speed.
"These things take time," said Allen.
"It was a difficult period for everyone in Welsh football but recent performances and results show we are moving in the right direction.
"We have always had the talent and ability that's for sure.
"Now we are getting to the stage where we are benefiting from past experiences and we are ready to take it to the next level."