He stated that Flekken was sidelined with an injury, forcing a change in goal.
Hákon Valdimarsson stepped in as his replacement during the 2-0 loss to Spurs at Gtech Community Stadium.
"He had a side strain," said the Bees boss to reporters.
"Let's see, we have two weeks now until the next game. Hopefully, he'll be back for West Ham.
"I thought it was a solid performance from Hákon."
Frank added on the game: "It feels like we missed an opportunity to get three points.
“In many ways, it was a good performance, without it being a through-the-roof performance - we created so many opportunities and good situations without having enough cutting edge to create five or six 100-per-cent chances.
“We created more than enough to score at least one goal, and then it would have been a different game - that’s frustrating because it’s such small things that decide a match.
“For example, their first goal… we hadn’t conceded from a corner all season. It happens, it is what it is, we had plenty of time to get back into the game but we couldn’t do that.”