The pair and team-mate Rory Sutherland will link up with the Lions at their training camp in Jersey a week on Sunday as preparations begin in earnest for the tour of South Africa.
Watson has not played since being named in Warren Gatland’s squad on May 6 but has recovered from a groin issue and will start against Ulster as Edinburgh play their final match as permanent residents of BT Murrayfield before moving to their new stadium on the back pitches.
Glasgow Warriors omitted their two Lions, Ali Price and Zander Fagerson, for Friday night’s game with Leinster but Richard Cockerill believes Watson and van der Merwe will benefit from a return to action. Sutherland is still recovering from a shoulder injury.
“Hamish and Duhan both want to play to get a bit of game time before they go to Jersey,” said the Edinburgh coach. “They won’t play next week [against Scarlets]. They’re fit, and they probably need the minutes under their belt to make sure they’re match sharp and trying to compete for a Test spot.”
Cockerill said he had talked with the pair about their participation in the Ulster game and intends for them both to play the full match, all being well.
“They don’t want to be undercooked,” said the coach. “Yeah, there were discussions over making sure they are in the best position to go to the Lions and ready to put their best foot forward to get in the Test team.
“The players want to play 80 minutes because they need the time. If we have any issues, or either of them feel compromised, certainly in Hamish’s case, I will be probably be looking after him because he certainly plays in a position that is attritionally a little bit harder than Duhan’s.”
Cockerill said that Sutherland was making good progress from the dislocated shoulder he sustained in Scotland’s win over France in Paris in March.
“I think he will arrive in Jersey fully fit and ready to participate in all training and playing,” Cockerill said of the prop.
The Ulster match is a dead rubber in terms of the Rainbow Cup and Edinburgh will give a debut to 19-year-old full-back Harry Paterson. Fellow teenagers Patrick Harrison and
Ben Muncaster have also been selected, at hooker and No 8 respectively. All three were named in the Scotland squad this week for the Under-20 Six Nations.
A positive Covid case at the club means Edinburgh are without half a dozen players for their final home match of the season.
The end of what has been a disappointing campaign can’t come quickly enough for Cockerill.
“This year has been difficult, there is no mistaking that and we need to press the reset button in the summer and revisit some of the things that have made the club so good in the first three years of being together,” he said.
“We will be happy to be in a new stadium, getting more identity and building a club. Building our supporter base is fundamental to what the club is going to be based on in the future.”