Eddie Jones will on Thursday roll the dice and name an England squad missing 20 frontline players – including a number of British & Irish Test Lions – for the summer tour of South Africa.

Dylan Hartley, Jonathan Joseph and Anthony Watson are among those already ruled out through injury – but including those Jones believes are in need of a rest it is understood he considers 20 players “unavailable”, such is the toll of a gruelling post-Lions season.

Jones has stressed the impact that the British & Irish Lions tour has had on his squad – 15 Englishmen toured New Zealand – though the absence, enforced or by design, of such a large number of players calls into question the relationship between club and country, and the workload placed on international players.

Indeed on Wednesday the Rugby Players’ Association board was due to discuss proposed changes to the season structure, thought to involve a two-week extension.

Nonetheless the 34-man squad will represent Jones’s boldest selection to date, despite England’s three‑match losing run and their worst Six Nations finish. Jones has acknowledged he should have freshened things up earlier and while he considers his hand forced to a degree, he will follow through with his squad for South Africa.

On top of the touring party for the three‑Test series against the Springboks, Jones will also unveil on Thursday Hartley’s replacement as captain as well as a 31-man squad for next week’s training camp in Brighton, which will be significantly different because of the absences of players from the four Premiership semi-finalists.

Jones will not rest his entire Lions contingent – Owen Farrell remains the favourite for the captaincy after he was rested during the autumn internationals and Mako Vunipola will also travel – but Dan Cole is among those expected to be omitted.

The number of absences also opens the door for a host of fringe players to stake claims against South Africa while Billy Vunipola, despite his recent hamstring injury, is available to return to the international fold. He was absent from Saracens’ win against Gloucester last weekend and is yet to start for the club since breaking an arm in January, but the latest indications are that he will return for their Premiership semi‑final against Wasps.

Jones was also on Wednesday night mulling over a recall for Danny Cipriani, who has not played for England since 2015 but whose fine form towards the end of the season had brought him into the head coach’s thinking. Cipriani’s club future appears to hang on whether or not he is included. He is yet to announce where he will play next season after finishing the current campaign with Wasps but if Jones omits him again, he is expected to move abroad.

Jones was also set to make a call on the Hurricanes flanker Brad Shields, who last month lodged a request with New Zealand Rugby (NZR) to be released for the tour after the Guardian revealed he was eligible for selection in the eyes of the Rugby Football Union.

The Hurricanes flanker Brad Shields may also be picked for the South Africa tour. Photograph: Photosport/INPHO/REX/Shutterstock

New Zealand are yet to publicly state whether they have accepted Shields’s request for release for the tour but it is understood NZR and the Rugby Football Union have been in talks.

The 31-man training squad will feature players from the eight Premiership clubs not involved in the playoffs; those from the losing semi-finalists will join the following week and come into contention to face the Barbarians on 27 May at Twickenham.

South Africa will face Wales in Washington DC on 2 June before the first Test against England a week later in Johannesburg but they will do so without their influential hooker Malcolm Marx, who has been ruled out for six weeks with a hamstring tear.

His absence is a bitter blow for the Springboks considering Marx was named South Africa’s player of the year in 2017 and has established himself as one of the world’s leading hookers.