The attacker was recalled by Sunderland during January as the Black Cats struggled with Covid-19 and injury issues.
But Diamond has now returned to Harrogate Town and is set to play for the League Two outfit until the rest of the season.
"I think having a bit of a rest could have benefited Jack," Town boss Weaver said.
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"We are coming up to a very busy period of the season, the workload is going to be heavy over the coming months.
"I think any player benefits from the chance to recharge the batteries when they've been playing a lot of minutes on a regular basis.
"But, he's been outstanding for us and I thought he did very well in the game he started for Sunderland the other week.
"Particularly in the first half, he had good League One opposition on the back foot as he looked to run with the ball as he does and really take the game to them."
Charlton Athletic secure Premier League loan
Charlton have secured the loan signing of England youth international Nile John from Tottenham Hotspur until the end of the season.
The 18-year-old is highly rated at Spurs with ex-Charlton boss and current Tottenham coach Chris Powell helping to broker the deal
Speaking to the club’s website, John said: "I'm over the moon, I’m really looking forward to it. I’m really excited to get out there and play for the fans and play for the badge.
“Chris Powell is someone who I confide in – this connection with Charlton that he’s had and the history and how the fans have been, how the whole club is as a unit, allowed me to feel more welcomed. I’m really grateful for Chris that we’ve got this connection, this link together.”
Owner Thomas Sandgaard added: “We have been really impressed with what we have seen while monitoring Nile. He is young, talented, energetic, creative and possesses a lot of attacking quality. I am looking forward to watching him playing for Charlton.”
The centre midfielder becomes the Addicks' third signing of the January transfer window after the arrivals of Chuks Aneke and Juan Castillo.