Albion this week recruited winger Sinclair on a season-long loan from Manchester City with a view to a permanent move.
He switched from Swansea to the Blues a year ago, but then made only three starts last term.
The 24-year-old represented Great Britain at the 2012 London Olympics and has played at various youth levels for England.
And on the possibility of Sinclair progressing to the senior Three Lions set-up over the coming months, Clarke said: "World Cup year - can he be part of the squad? Yes, why not?
"He's a winger who can create and score goals. Why can't he be part of that World Cup squad? He has a lot to play for this year.
"He obviously has great potential, otherwise a club like Manchester City wouldn't splash out the money for him.
"I think there are some places open in the England squad. In football a week's a long time, never mind six months or a year for someone to force their way into the plans and go to the World Cup."
Sinclair is set to make his West Brom debut in Saturday's Barclays Premier League clash with Everton at Goodison Park.
Clarke said: "He had a couple of great seasons at Swansea, got the big-money move to Manchester City and he feels he didn't get the chances that he deserved to play in their team, and I think he is probably right on that.
"He comes here hungry and determined to prove he is still the quality player he showed he was at Swansea. He is desperate to play this weekend."
A summer signing who will not be involved for the Baggies on Saturday is Nicolas Anelka, who has been granted indefinite compassionate leave by the club following the death of his agent Eric Manasse last weekend.
Clarke has confirmed the 34-year-old former France striker spoke to him and Albion sporting and technical director Richard Garlick about retiring from football altogether on Thursday before departing West Brom's training ground.
And asked on Friday if he fully expected to see Anelka playing for the midlands outfit again, Clarke said: "Fully expect? I don't know, because from the conversation we had the other day, it was really negative.
"But we have given him time to think about it. So I'd like to think he could play for West Bromwich Albion again."
Asked directly if Anelka had mentioned quitting, Clarke said: "I'm not going to deny that he used that word in the conversations we had with him."
Clarke has stressed there was no "bust-up" between Anelka and the club, that there will be further discussions between the two parties in due course, and that an injury the frontman sustained on his competitive Albion debut last weekend - the 1-0 home league loss to Southampton - had already made it unlikely that he would feature against the Toffees.
The Scot has also emphasised that although he is looking for more new signings before the transfer window shuts, with certain unnamed targets "close", strikers are not at the top of his priority list.
Clarke, who as well as Sinclair and Anelka has added striker Matej Vydra (on loan) and defender Diego Lugano to his squad this summer, said: "I've got good players up front.
"Shane Long is a mainstay of the team. He was last season, he will be again this season.
"I've brought in Matej Vydra, who has been electric in training.
"Markus Rosenberg has had a great pre-season and is looking forward to showing everybody he can cut it in the Premier League.
"So I've got three forwards already for Saturday who have a lot to prove and are desperate to prove it.
"At the moment in that position I think I'm okay."