Portsmouth will look to close the gap on the top two in London three south west by beating Old Tiffinians at Rugby Camp.
The hosts are six points behind second-placed Old Emanuel and 10 adrift of leaders Old Cranleighans.
However, both visit Portsmouth before the end of the season.
‘This is a match we need to win,’ said director of rugby Jim Pearce.
‘In recent games we have been guilty of taking our foot off the gas at times.
‘That is something we can’t afford to keep doing – particularly if we want to pick up bonus points.
‘We are also looking to retain our unbeaten home record.’
Jack Easterbrook replaces the unavailable Will Brock in the back row.
Simon Morgan reverts to scrum-half and Gareth Richards is at outside-half.
United Services put their unbeaten Hampshire one record on the line as they travel to third-placed Millbrook.
Services hold a 15-point lead at the top.
In Hampshire two, Southsea Nomads head to the north of the county to take on Farnborough.
Hampshire under-20s face a decisive game against Gloucestershire on Sunday – with a place in the quarter-finals of the Jason Leonard Under-20 County Championship at stake.
It is a winner-takes-all encounter at Hooks Lane in Havant (2pm).
Hampshire are looking to claim a quarter-final place for the second successive season.
The county have beaten Dorset and Wiltshire and lost at Cornwall.
Hampshire are boosted by the return of Havant prop Elliot Bellman and second-row forward Ed Grinsted.
Petersfield’s Nick Blumlein has recovered from concussion to take the fly-half berth.
Entry at Hooks Lane is free and manager Mike Greenslade is hoping for a big crowd.
He said: ‘Gloucestershire will be strong opponents and we have similar records.
‘There is a huge amount riding on the result, so a big crowd would be appreciated to try to help the lads get over the line.’