Foreach with references

Is it possible to use a foreach with references, to optimize the loop?

private function getClientUnPaidSettlements() {                                     
    $settlements = ClientSummary::query()->getUnPaidSettlement()->get();                
    $cTx = new ClientTransaction();                                                     
    foreach($settlements as $settlement){                               
        $settlement->txs = $cTx->getUnsettledNew($settlement->currency);
    }
    return $settlements;                                                                
}