England scrum-half Ben Youngs may have to wait until the autumn for his 100th cap, with player welfare rules set to bar him from July's tour of Japan.

Regulations state any England World Cup squad member should be rested for the two-Test trip, unless they have fewer than 20 match involvements this season.

A match involvement is defined as any appearance of more than 20 minutes in a game.

Youngs has already played in 20 games for club and country since August.

The 30-year-old won his 99th England cap against Wales last weekend.

He has been denied a chance to reach his century this month, with England's Six Nations finale against Italy in Rome called off because of coronavirus.

With England boss Eddie Jones set to take an inexperienced squad to Japan, Youngs is now unlikely to reach the milestone until later in the year, but says he has no plans to relinquish his hold on the number nine shirt.

"I am only 30 and have unbelievable ambition to play for England," he told BBC Radio 5 Live following his man-of-the match display in the 33-30 victory at Twickenham.

"As long as I stay fit, touch wood, and keep trying to improve, hopefully I will get an opportunity to keep playing in the shirt."

The definition of a match involvement was outlined in an agreement signed by the Premiership, RFU and players' union (RPA) in October 2018.

While a number of England's key players are therefore likely to be unavailable for the tour, the relevant parties are able to make "individual exceptions" to the welfare policy.

Head coach Jones says he has already started looking forward to the series against the World Cup quarter-finalists.

"We are looking forward to getting together and playing against Japan - which will be tough," Jones told BBC Radio 5 Live.

"We are playing in Oita, which is going to be 35 degrees and 85% humidity. They will have four months' preparation and we will have one week, so we are looking forward to that, which will be our next outing."