Who played Seeker for Gryffindor during the final game in Philosopher's Stone?

Question

Whilst preparing an answer for another question about the Gryffindor Quidditch team I realised that I didn't know who filled Harry's place in the final game of the season in Philosopher's Stone. I just put "unknown player". Has it ever been stated who that player was?

We know that the Gryffindor vs. Ravenclaw game went ahead without Harry, who was still recovering in the sick bay after his confrontation with Quirrell.

"Listen, you've got to be up for the end-of-year feast tomorrow. The points are all in and Slytherin won, of course - you missed the last Quidditch match, we were steamrollered by Ravenclaw without you - but the food'll be good."
_{(Philosopher's Stone, Chapter 17, The Man With Two Faces).}

We know that Gryffindor didn't have a huge range of backup Seekers since Wood didn't appoint anyone at the trials that year. But presumably they played somebody.

Who was it?

---

I've just found the following quote, which implies that Harry believed that Gryffindor wouldn't be able to play at all without him since there was no replacement Seeker.

Speaking quietly so that no one else would hear, Harry told the other two about Snape's sudden, sinister desire to be a Quidditch referee.
"Don't play," said Hermione at once.
"Say you're ill," said Ron.
"Pretend to break your leg," Hermione suggested.
"Really break your leg," said Ron.
"I can't," said Harry. "There isn't a reserve Seeker. If I back out, Gryffindor can't play at all."
_{(Philosopher's Stone, Chapter 13, Nicolas Flamel).}

Answer 1

We don't know. Maybe no one.

This event is only mentioned twice in the books

"Listen, you’ve got to be up for the end-of-year feast tomorrow. The points are all in and Slytherin won [the House Cup], of course – you missed the last Quidditch match, we were steamrollered by Ravenclaw without you – but the food’ll be good."
_{The Philosopher's Stone - Chapter 17: The Man with Two Faces}

‘Now, listen here, you lot,’ [Wood] said, glowering at them all, ‘we should have won the Quidditch Cup last year. We’re easily the best team. But unfortunately, owing to circumstances beyond our control...’

Harry shifted guiltily in his seat. He had been unconscious in the hospital wing for the final match of the previous year, meaning that Gryffindor had been a player short and had suffered their worst defeat in three hundred years.
_{The Chamber of Secrets - Chapter 7: Mudbloods and Murmurs}

Neither instance mentions who subbed in. Charlie Weasley had graduated the year before, so Gryffindor didn't have anyone else who had played Seeker in the past to step up. Given the way it is worded, one could even infer that Gryffindor only fielded 6 people for that game.

Since it was "their worst defeat in three hundred years", it would be a much worse defeat than a normal game where they didn’t catch the snitch. Which implies that they were severely lacking in either the position of Keeper or Chaser. Since Wood doesn’t grumble about having to play Seeker, and Ron doesn’t mention it to Harry (as he almost certainly would), we can only assume that one of the Chasers played the position of Seeker and Gryffindor either had a random person fill in as Chaser, or they played one Chaser down (would would align with the whole “worst defeat” thing).

Answer 2

During a conversation before the first Quidditch match in Harry Potter and the Chamber of Secrets, while Oliver Wood was going over tactics when they were changing for their first practice session, we see this line:

...He had been unconscious in the hospital wing for the final match of the previous year meaning that Gryffindor had been a player short and had suffered their worst defeat in 300 years.
_{Harry Potter and the Chamber of Secrets, chapter 7}

This silences any speculation on the matter by answering definitively that they were a player short.

Answer 3

There isn't an official canon answer as far as I know, but we can apply a bit of guesswork. The next time after book 1 that a Quidditch match happened without Harry was book 5, when Umbridge bans Harry from Quidditch. Thereafter Ginny is Seeker until the ban is revoked for book 6. Obviously Ginny could not have played the last Quidditch match in PS because she wasn't even at Hogwarts yet.

The only other likely source of Seekers is from the team previous to Harry's first year at Hogwarts. We know that Oliver Wood, Fred, and George were on that team, and Alicia Spinnet was only on reserve. That year, Gryffindor was "flattened" by Slytherin according to McGonagall, so whoever was Seeker that year was probably not very good. My guess is that either the Seeker from the previous year was brought back or another player was brought back, and one of the other current players was Seeker. The latter seems more likely, as when McGonagall recruits Harry, she says to Oliver Wood, "Wood - I've found you a Seeker." That would be odd to say if the Seeker from the previous year was still around, so he or she probably graduated.

So, short answer based on speculation:

A player from the previous year came in to replace one of Harry's teammates, who in turn replaced Harry as the Seeker.