The South African international is entangled in a messy transfer wrangle with the Tshwane outfit over his desire to further his career in Europe, with the club reluctant to let him go.
Last season Mphela came close to signing for Russian side Terek Grozny, a team now managed by Dutch legend Ruud Gullit, while Birmingham City in the English Premier League and Scottish giants Rangers were also tracking the forward's progress.
While moves failed to materialise to any of those clubs, Mphela has now fallen out with Sundowns after they rejected a bid - reported to be in the region of R15million - from Serbian champions Partizan.
To protest against the Brazilians' unwillingness to consider that offer, a recalcitrant Mphela has skipped a number of training sessions at Chloorkop.
Booth, however, who spent several years in Russia with Rostov and Krylia Sovetov, told The Sunday Times that he is sympathetic towards 'Killer'.
"For that sole reason [staying fit], I would advise him to get back to training," said Booth.
"But I understand his frustration, because a good offer from a Champions League club doesn't come along every day. He's been a stalwart for us, providing a lot of confidence, so hopefully he can sort it out."
Mphela, 26, is eager to have another opportunity to play abroad. Earlier in his career the Brits-born player had spells with RC Strasbourg and Stade Reims, but failed to settle or make an impact in French football in the 2004/5 and 2005/6 seasons.
Mphela subsequently returned to South Africa in 2006 after signing a deal with SuperSport United and made the short move to Sundowns two years later.